Exhibit 99.1

FOR IMMEDIATE RELEASE

PROSPERITY BANCSHARES, INC.®

REPORTS SECOND QUARTER

2023 EARNINGS

HOUSTON, July 26, 2023. Prosperity Bancshares, Inc.® (NYSE: PB), the parent company of Prosperity Bank® (collectively, “Prosperity”), reported net income of $86.9 million for the quarter ended June 30, 2023 compared with $128.5 million for the same period in 2022. Net income per diluted common share was $0.94 for the quarter ended June 30, 2023 compared with $1.40 for the same period in 2022. On May 1, 2023, First Bancshares of Texas, Inc. (“First Bancshares”) merged with Prosperity Bancshares and FirstCapital Bank of Texas, N.A. (“FirstCapital Bank”) merged with Prosperity Bank (collectively, the “Merger”). During the second quarter of 2023, Prosperity incurred a merger related provision for credit losses of $18.5 million, or $0.16(1) per diluted common share, and merger related expenses of $12.9 million, or $0.11(1) per diluted common share. Excluding these charges, earnings per diluted common share was $1.21(1) for the second quarter of 2023. Additionally, loans, excluding Warehouse Purchase Program loans, increased $1.970 billion or 10.6% during the second quarter of 2023, primarily due to the Merger. The annualized return on second quarter average assets was 0.89%, and the annualized return on second quarter average assets excluding merger related provision for credit losses, net of tax, and merger related expenses, net of tax was 1.14%(1). Nonperforming assets remain low at 0.18% of second quarter average interest-earning assets.

“I am pleased to announce that on May 1, 2023, Prosperity completed the merger of First Bancshares of Texas and its wholly owned subsidiary FirstCapital Bank, headquartered in Midland, Texas. FirstCapital Bank operated 16 full-service banking offices in six different markets in West, North and Central Texas areas, including its main office in Midland, and banking offices in Midland, Lubbock, Amarillo, Wichita Falls, Burkburnett, Byers, Henrietta, Dallas, Horseshoe Bay, Marble Falls and Fredericksburg, Texas,” said David Zalman, Prosperity’s Senior Chairman and Chief Executive Officer.

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“For the second quarter of 2023, Prosperity’s net income was impacted by merger related charges. Excluding those charges, our earnings remain strong but are lower than previous quarters, primarily because of the timing differences in that our cost of funds has increased faster than our earning assets have repriced. The good news is that based on our models, we show our net interest margin improving in a 12 month and 24-month time period to more normal levels. However, if rates increase more than we anticipate, this could change. Together with our model projections, strong capital position, liquidity, earnings, strong cost controls and sound asset quality, we believe opportunities remain for continued growth and expansion. I would like to welcome our new associates and thank our current associates for the all the hard work and integrity they show every day taking care of our customers,” concluded Zalman.

Results of Operations for the Three Months Ended June 30, 2023

Net income was $86.9 million(2) for the three months ended June 30, 2023 compared with $128.5 million(3) for the same period in 2022, and was impacted by merger related provision for credit losses of $18.5 million and merger related expenses of $12.9 million. Net income per diluted common share was $0.94 for the three months ended June 30, 2023 compared with $1.40 for the same period in 2022, and was also impacted by merger related provision and expenses. On a linked quarter basis, net income was $86.9 million(2) for the three months ended June 30, 2023 compared with $124.7 million(4) for the three months ended March 31, 2023. The change was primarily due to the Merger. Net income per diluted common share was $0.94 for the three months ended June 30, 2023 compared with $1.37 for the three months ended March 31, 2023. Annualized returns on average assets, average common equity and average tangible common equity for the three months ended June 30, 2023 were 0.89%, 5.01% and 9.67%(1), respectively. Excluding merger related provision for credit losses, net of tax, and merger related expenses, net of tax, annualized returns on average assets, average common equity and average tangible common equity for the three months ended June 30, 2023 were 1.14%(1), 6.45%(1) and 12.43%(1), respectively. Prosperity’s efficiency ratio (excluding net gains and losses on the sale or write down of assets and securities) was 53.21%(1) for the three months ended June 30, 2023; and excluding merger related expenses, the efficiency ratio was 48.51%(1).

Net interest income before provision for credit losses for the three months ended June 30, 2023 was $236.5 million compared with $248.5 million for the same period in 2022, a decrease of $12.0 million or 4.8%. The change was primarily due to an increase in average balances and rates on borrowings and an increase in the average rates on interest-bearing deposits, partially offset by an increase in the average balances and average rates on loans held for investment and an increase in average rates on investment securities. On a linked quarter basis, net interest income before provision for credit losses was $236.5 million compared with $243.5 million for the three months ended March 31, 2023, a decrease of $7.0 million or 2.9%. The change was primarily due to an increase in the average balances and average rates on other borrowings, an increase in average rates on interest-bearing deposits and a decrease in average federal funds sold and other earning assets, partially offset by an increase in the average balances and average rates on loans.

The net interest margin on a tax equivalent basis was 2.73% for the three months ended June 30, 2023 compared with 2.97% for the same period in 2022. The change was primarily due to an increase in average balances and average rates on borrowings and an increase in the average rates on interest-bearing deposits, partially offset by an increase in the average balances and average rates on loans held for investment and an increase in average rates on investment securities. On a linked quarter basis, the net interest margin on a tax equivalent basis was 2.73% for the three months ended June 30, 2023 compared with 2.93% for the three months ended March 31, 2023. The change was primarily due to an increase in the average balances and average rates on other borrowings, an increase in average rates on interest-bearing deposits and a decrease in average federal funds sold and other earning assets, partially offset by an increase in the average balances and average rates on loans.

Noninterest income was $39.7 million for the three months ended June 30, 2023 compared with $37.6 million for the same period in 2022, an increase of $2.1 million or 5.6%. On a linked quarter basis, noninterest income was $39.7 million compared with $38.3 million for the three months ended March 31, 2023, an increase of $1.4 million or 3.7%.

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Noninterest expense was $145.9 million for the three months ended June 30, 2023 compared with $122.9 million for the same period in 2022, an increase of $23.0 million or 18.7%. On a linked quarter basis, noninterest expense increased $22.9 million or 18.6% to $145.9 million compared with $123.0 million for the three months ended March 31, 2023. The change for both periods was primarily due to an increase in merger related expenses, an increase in salaries and benefits and an increase in additional expenses related to two months of FirstCapital Bank operations.

Results of Operations for the Six Months Ended June 30, 2023

Net income was $211.6 million(5) for the six months ended June 30, 2023 compared with $250.8 million(6) for the same period in 2022, and was impacted by merger related provision for credit losses of $18.5 million and merger related expenses of $13.8 million. Net income per diluted common share was $2.30 for the six months ended June 30, 2023 compared with $2.73 for the same period in 2022, and was also impacted by merger related provision and expenses. Annualized returns on average assets, average common equity and average tangible common equity for the six months ended June 30, 2023 were 1.09%, 6.18% and 11.97%(1), respectively. Excluding merger related provision for credit losses, net of tax, and merger related expenses, net of tax, annualized returns on average assets, average common equity and average tangible common equity for the six months ended June 30, 2023 were 1.22%(1), 6.93%(1) and 13.41%(1), respectively. Prosperity’s efficiency ratio (excluding net gains and losses on the sale or write down of assets and securities) was 48.38%(1) for the six months ended June 30, 2023; excluding merger related expenses, the efficiency ratio was 45.90% (1).

Net interest income before provision for credit losses for the six months ended June 30, 2023 was $479.9 million compared with $488.4 million for the same period in 2022, a decrease of $8.5 million or 1.7%. The change was primarily due to an increase in the average balances and average rates on other borrowings and an increase in average rates on interest-bearing deposits, partially offset by increases in the average balances and increases in average rates on loans held for investment and on investment securities.

The net interest margin on a tax equivalent basis for the six months ended June 30, 2023 was 2.83% compared with 2.92% for the same period in 2022. The changes were primarily due to an increase in the average balances and average rates on interest-bearing liabilities, partially offset by an increase in average balances and average rates on loans and an increase in average rates on investment securities.

Noninterest income was $78.0 million for the six months ended June 30, 2023 compared with $72.7 million for the same period in 2022, an increase of $5.2 million or 7.2%, primarily due to increases in trust income, credit card, debit card and ATM income and other noninterest income.

Noninterest expense was $268.9 million for the six months ended June 30, 2023 compared with $242.7 million for the same period in 2022, an increase of $26.1 million or 10.8%. The change was primarily due to $13.8 million of merger related expenses, an increase in Federal Deposit Insurance Corporation assessments of $4.4 million and an increase in additional expenses related to two months of FirstCapital Bank operations.

Balance Sheet Information

At June 30, 2023, Prosperity had $39.905 billion in total assets, an increase of $2.518 billion or 6.7%, compared with $37.387 billion at June 30, 2022.

Loans were $21.654 billion at June 30, 2023, an increase of $2.320 billion or 12.0% from $19.334 billion at March 31, 2023. Loans increased $3.445 billion or 18.9% compared with $18.209 billion at June 30, 2022. Loans, excluding Warehouse Purchase Program loans, were $20.505 billion at June 30, 2023 compared to $18.535 billion at March 31, 2023, an increase of $1.970 billion or 10.6%, and compared to $17.071 billion at June 30, 2022, an increase of $3.434 billion or 20.1%.

Deposits were $27.381 billion at June 30, 2023, an increase of $376.7 million or 1.4% compared with $27.004 billion at March 31, 2023. Deposits decreased $2.485 billion or 8.3%, compared with $29.866 billion at June 30, 2022, primarily due to a decrease in public fund deposits and business deposits, partially offset by an increase in Merger acquired deposits.

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The table below provides detail on the impact of loans acquired and deposits assumed in the Merger.

Excluding loans acquired in the Merger and new production by the acquired lending operations since May 1, 2023, loans at June 30, 2023 grew $729.5 million or 3.8% compared with March 31, 2023 and $1.855 billion or 10.2% compared with June 30, 2022. Excluding loans acquired in the Merger and new production by the acquired lending operations since May 1, 2023 and Warehouse Purchase Program loans, loans at June 30, 2023 grew $379.7 million or 2.0% (8.2% annualized) compared with March 31, 2023 and $1.844 billion or 10.8% compared with June 30, 2022.

Excluding deposits assumed in the Merger and new deposits generated at the acquired banking centers since May 1, 2023, deposits at June 30, 2023 decreased by $1.105 billion or 4.1% compared with March 31, 2023 and decreased by $3.967 billion or 13.3% compared with June 30, 2022.

Asset Quality

Nonperforming assets totaled $62.7 million or 0.18% of quarterly average interest-earning assets at June 30, 2023 compared with $22.2 million or 0.07% of quarterly average interest-earning assets at June 30, 2022 and $24.5 million or 0.07% of quarterly average interest-earning assets at March 31, 2023. The increase during the second quarter of 2023 was primarily due to the Merger and two loans that were placed on nonaccrual status during the quarter, one of which is under contract for sale.

The allowance for credit losses on loans and off-balance sheet credit exposures was $381.7 million at June 30, 2023 compared with $313.9 million at June 30, 2022 and $312.1 million at March 31, 2023. The provision for credit losses was $18.5 million for the three and six months ended June 30, 2023 compared to no provision for credit losses for the three and six months ended June 30, 2022. As a result of the loans acquired in the Merger, the second quarter of 2023 included a $12.0 million provision for credit losses on loans and a $6.5 million provision for credit losses on off-balance sheet credit exposures.

The allowance for credit losses on loans was $345.2 million or 1.59% of total loans at June 30, 2023 compared with $284.0 million or 1.56% of total loans at June 30, 2022 and $282.2 million or 1.46% of total loans at March 31, 2023. Excluding Warehouse Purchase Program loans, the allowance for credit losses on loans to total loans was 1.68%(1) at June 30, 2023 compared with 1.66%(1) at June 30, 2022 and 1.52%(1) at March 31, 2023.

Net charge-offs were $16.1 million for the three months ended June 30, 2023 compared with net charge-offs of $1.2 million for the three months ended June 30, 2022 and net recoveries of $615 thousand for the three months ended March 31, 2023. Net charge-offs for the second quarter of 2023 included $15.0 million related to one commercial real estate loan obtained in a previous merger. Additionally, $3.5 million of specific reserves on resolved purchased credit deteriorated ("PCD") loans without any related charge-offs was released to the general reserve.

Net charge-offs were $15.5 million for the six months ended June 30, 2023 compared with $2.4 million for the six months ended June 30, 2022. Net charge-offs for the six months ended June 30, 2023 included $15.0 million related to one commercial real estate loan obtained in a previous merger. Additionally, $3.7 million of specific reserves on resolved PCD loans without any related charge-offs was released to the general reserve.

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Dividend

Prosperity Bancshares declared a third quarter 2023 cash dividend of $0.55 per share to be paid on October 2, 2023, to all shareholders of record as of September 15, 2023.

Stock Repurchase Program

On January 17, 2023, Prosperity Bancshares announced a stock repurchase program under which up to 5%, or approximately 4.6 million shares, of its outstanding common stock may be acquired over a one-year period expiring on January 17, 2024, at the discretion of management. Under its 2023 stock repurchase program, Prosperity Bancshares repurchased approximately 595 thousand shares of its common stock at an average weighted price of $57.49 per share during the three months ended June 30, 2023 and approximately 1.21 million shares of its common stock at an average weighted price of $59.88 per share during the six months ended June 30, 2023.

Merger of First Bancshares of Texas, Inc.

On May 1, 2023, Prosperity completed the merger of First Bancshares and its wholly owned subsidiary FirstCapital Bank, headquartered in Midland, Texas. FirstCapital Bank operated 16 full-service banking offices in six different markets in West, North and Central Texas areas, including its main office in Midland, and banking offices in Midland, Lubbock, Amarillo, Wichita Falls, Burkburnett, Byers, Henrietta, Dallas, Horseshoe Bay, Marble Falls and Fredericksburg, Texas.

Pursuant to the terms of the definitive agreement, Prosperity issued 3,583,370 shares of Prosperity common stock plus approximately $91.5 million in cash for all outstanding shares of First Bancshares, which resulted in goodwill of $152.1 million as of June 30, 2023. Additionally, Prosperity recognized $25.3 million of core deposit intangibles as of June 30, 2023. The goodwill balance as of June 30, 2023 does not include subsequent fair value adjustments that are still being finalized. During the second quarter of 2023, Prosperity completed the operational conversion of FirstCapital Bank.

Pending Merger of Lone Star State Bancshares, Inc.

On October 11, 2022, Prosperity Bancshares and Lone Star State Bancshares, Inc. (“Lone Star”) jointly announced the signing of a definitive merger agreement whereby Lone Star, the parent company of Lone Star State Bank of West Texas (“Lone Star Bank”) will merge with and into Prosperity. Lone Star Bank operates 5 banking offices in the West Texas area, including its main office in Lubbock, and 1 banking center in each of Brownfield, Midland, Odessa and Big Spring, Texas. As of June 30, 2023, Lone Star, on a consolidated basis, reported total assets of $1.276 billion, total loans of $1.072 billion and total deposits of $1.117 billion.

Under the terms of the merger agreement, Prosperity will issue 2,376,182 shares of Prosperity common stock plus $64.1 million in cash for all outstanding shares of Lone Star capital stock, subject to certain conditions and potential adjustments. Based on Prosperity’s closing price of $69.27 on October 7, 2022, the total consideration was valued at approximately $228.7 million. The transaction is subject to customary closing conditions, including the receipt of regulatory approvals. The shareholders of Lone Star approved the transaction on March 28, 2023. The transaction is expected to close during the third quarter of 2023, although delays could occur.

Conference Call

Prosperity’s management team will host a conference call on Wednesday, July 26, 2023, at 11:30 a.m. Eastern Time (10:30 a.m. Central Time) to discuss Prosperity’s second quarter 2023 earnings. Individuals and investment professionals may participate in the call by dialing 877-885-0477 for domestic participants, or 412-902-6506 for international participants. The participant elite entry number is 7557443.

Alternatively, individuals may listen to the live webcast of the presentation by visiting Prosperity’s website at www.prosperitybankusa.com. The webcast may be accessed from Prosperity’s Investor Relations page by selecting “Presentations, Webcasts & Calls” from the menu and following the instructions.

Non-GAAP Financial Measures

Prosperity’s management uses certain non-GAAP financial measures to evaluate its performance. Specifically, Prosperity reviews diluted earnings per share excluding merger related provision for credit losses, net of tax, and merger related expenses, net of tax; return on average assets excluding merger related provision for credit losses, net of tax, and merger related expenses, net of tax; return on average common equity excluding merger related provision for credit losses, net of tax, and merger related expenses, net of tax; return on average tangible common equity; return on average tangible common equity excluding merger related provision for credit losses, net of tax, and merger related expenses, net of tax; tangible book value per share; the tangible equity to tangible assets ratio;

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allowance for credit losses to total loans excluding Warehouse Purchase Program loans; the efficiency ratio, excluding net gains and losses on the sale or write down of assets and securities; and the efficiency ratio, excluding net gains and losses on the sale or write down of assets and securities and merger related expenses, for internal planning and forecasting purposes. Prosperity believes these non-GAAP financial measures provide information useful to investors in understanding Prosperity’s financial results and their presentation, together with the accompanying reconciliations, provides a more complete understanding of factors and trends affecting Prosperity’s business and allows investors to view performance in a manner similar to management, the entire financial services sector, bank stock analysts and bank regulators. Further, Prosperity believes that these non-GAAP financial measures provide useful information by excluding certain items that may not be indicative of its core operating earnings and business outlook. These non-GAAP financial measures should not be considered a substitute for, nor of greater importance than, GAAP basis financial measures and results; Prosperity strongly encourages investors to review its consolidated financial statements in their entirety and not to rely on any single financial measure. Because non-GAAP financial measures are not standardized, it may not be possible to compare these financial measures with other companies’ non-GAAP financial measures having the same or similar names. Please refer to the “Notes to Selected Financial Data” at the end of this Earnings Release for a reconciliation of these non-GAAP financial measures to the nearest respective GAAP financial measures.

Prosperity Bancshares, Inc. ®

As of June 30, 2023, Prosperity Bancshares, Inc.® is a $39.905 billion Houston, Texas based regional financial holding company providing personal banking services and investments to consumers and businesses throughout Texas and Oklahoma. Founded in 1983, Prosperity believes in a community banking philosophy, taking care of customers, businesses and communities in the areas it serves by providing financial solutions to simplify everyday financial needs. In addition to offering traditional deposit and loan products, Prosperity offers digital banking solutions, credit and debit cards, mortgage services, retail brokerage services, trust and wealth management, and treasury management.

Prosperity currently operates 285 full-service banking locations: 65 in the Houston area, including The Woodlands; 30 in the South Texas area including Corpus Christi and Victoria; 62 in the Dallas/Fort Worth area; 22 in the East Texas area; 32 in the Central Texas area including Austin and San Antonio; 44 in the West Texas area including Lubbock, Midland-Odessa, Abilene; Amarillo and Wichita Falls; 16 in the Bryan/College Station area, 6 in the Central Oklahoma area; 8 in the Tulsa, Oklahoma area.

Cautionary Notes on Forward-Looking Statements

“Safe Harbor” Statement under the Private Securities Litigation Reform Act of 1995: This release contains, and the remarks by Prosperity’s management on the conference call may contain, forward-looking statements within the meaning of the federal securities laws, including Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. From time to time, oral or written forward-looking statements may also be included in other information released to the public. Such forward-looking statements are typically, but not exclusively, identified by the use in the statements of words or phrases such as “aim,” “anticipate,” “believe,” “estimate,” “expect,” “goal,” “guidance,” “intend,” “is anticipated,” “is expected,” “is intended,” “objective,” “plan,” “projected,” “projection,” “will affect,” “will be,” “will continue,” “will decrease,” “will grow,” “will impact,” “will increase,” “will incur,” “will reduce,” “will remain,” “will result,” “would be,” variations of such words or phrases (including where the word “could,” “may,” or “would” is used rather than the word “will” in a phrase) and similar words and phrases indicating that the statement addresses some future result, occurrence, plan or objective. Forward-looking statements include all statements other than statements of historical fact, including forecasts or trends, and are based on current expectations, assumptions, estimates and projections about Prosperity Bancshares and its subsidiaries. These forward-looking statements may include information about Prosperity’s possible or assumed future economic performance or future results of operations, including future revenues, income, expenses, provision for loan losses, provision for taxes, effective tax rate, earnings per share and cash flows and Prosperity’s future capital expenditures and dividends, future financial condition and changes therein, including changes in Prosperity’s loan portfolio and allowance for loan losses, changes in deposits, borrowings and the investment securities portfolio, future capital structure or changes therein, as well as the plans and objectives of management for Prosperity’s future operations, future or proposed acquisitions, including the pending transaction with Lone Star, the future or expected effect of acquisitions on Prosperity’s operations, results of operations, financial condition, and future economic performance, statements about the anticipated benefits of each of the proposed transactions, and statements about the assumptions underlying any such statement. These forward‑looking statements are not guarantees of future performance and are based on expectations and assumptions Prosperity currently believes to be valid. Because forward-looking statements relate to future results and occurrences, many of which are outside of Prosperity’s control, they are subject to inherent uncertainties, risks and changes in circumstances that are difficult to predict. These risks and uncertainties include, but are not limited to whether Prosperity can: successfully identify acquisition targets and integrate the businesses of acquired companies and banks, including Lone Star; continue to sustain its current internal growth rate or total growth rate; provide products and services that appeal to its customers; continue to have access to debt and equity capital markets; and achieve its sales objectives. Other risks include, but are not limited to: the possibility that credit quality could deteriorate; actions of competitors; changes in laws and regulations (including changes in governmental interpretations of regulations and changes in accounting standards); the possibility that

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the anticipated benefits of an acquisition transaction, including the pending transaction with Lone Star, are not realized when expected or at all, including as a result of the impact of, or problems arising from, the integration of two companies or as a result of the strength of the economy and competitive factors generally; a deterioration or downgrade in the credit quality and credit agency ratings of the securities in Prosperity’s securities portfolio; customer and consumer demand, including customer and consumer response to marketing; effectiveness of spending, investments or programs; fluctuations in the cost and availability of supply chain resources; economic conditions, including currency rate, interest rate and commodity price fluctuations; and the effect, impact, potential duration or other implications of weather and climate-related events. Prosperity disclaims any obligation to update such factors or to publicly announce the results of any revisions to any of the forward-looking statements included herein to reflect future events or developments. These and various other factors are discussed in Prosperity’s Annual Report on Form 10-K for the year ended December 31, 2022, and other reports and statements Prosperity has filed with the Securities and Exchange Commission (“SEC”). Copies of the SEC filings for Prosperity may be downloaded from the Internet at no charge from http://www.prosperitybankusa.com.

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Prosperity Bancshares, Inc.®

Financial Highlights (Unaudited)

(In thousands)

(A) Includes $(3,393), $(4,399), $(4,396), $(296) and $1,517 in unrealized (losses) gains on available for sale securities for the quarterly periods ended June 30, 2023, March 31, 2023, December 31, 2022, September 30, 2022 and June 30, 2022, respectively.

(B) Includes $(2,681), $(3,476), $(3,473), $(234) and $1,198 in after-tax unrealized (losses) gains on available for sale securities for the quarterly periods ended June 30, 2023, March 31, 2023, December 31, 2022, September 30, 2022 and June 30, 2022, respectively.

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Prosperity Bancshares, Inc.®

Financial Highlights (Unaudited)

(In thousands)