Exhibit 99.1

FOR IMMEDIATE RELEASE

PROSPERITY BANCSHARES, INC.®

REPORTS FIRST QUARTER

2023 EARNINGS

HOUSTON, April 26, 2023. Prosperity Bancshares, Inc.® (NYSE: PB), the parent company of Prosperity Bank® (collectively, “Prosperity”), reported net income of $124.7 million for the quarter ended March 31, 2023 compared with $122.3 million for the same period in 2022. Net income per diluted common share was $1.37 for the quarter ended March 31, 2023 compared with $1.33 for the same period in 2022, an increase of 3.0%, and the annualized return on first quarter average assets was 1.31%. Additionally, loans, excluding Warehouse Purchase Program loans, increased $436.0 million or 2.4% (9.6% annualized) during the first quarter of 2023. Nonperforming assets remain low at 0.07% of first quarter average interest-earning assets.

“Prosperity continued to show strong earnings despite the failures of Silicon Valley Bank and Signature Bank and the overall pressures on the banking system. Net income was $124.7 million for the three months ended March 31, 2023, compared with $122.3 million for the same period in 2022, an increase of $2.4 million or 1.9%. Loans, excluding Warehouse Purchase Program loans, increased 9.6% annualized for the quarter, while nonperforming assets remained low at 0.07% of first quarter average interest-earning assets. Prosperity repurchased 611,263 of its shares in the first quarter. We are also pleased to announce that we received all necessary regulatory and shareholder approvals for the acquisition of First Bancshares of Texas, Inc.,” said David Zalman, Prosperity’s Senior Chairman and Chief Executive Officer.

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“As we all are aware, the market was flooded with excess funds the last few years during the COVID-19 pandemic and now the Federal Reserve is reducing the money supply in its efforts to lower inflation. In turn, most banks saw a loss of deposits during the quarter, including from some customers who were concerned with liquidity after the failure of SVB and Signature Bank. Prosperity has established lines of credit at the Federal Home Loan Bank and the Federal Reserve in the amount of $14.7 billion, of which $11.3 billion is currently available. This is approximately $4 billion in excess of our uninsured and pledged deposits,” added Zalman.

“Texas and Oklahoma continue to do well. Texas’ population increased by approximately 470,000 in 2022, continuing a steady uptick. From 2002 to 2022, Texas gained over 9 million residents, more than any other state and almost 3 million more than Florida, the next largest gaining state. Texas and Oklahoma continue to benefit from strong economies and are home to 56 Fortune 500 headquartered companies. Texas now has more Fortune 500 companies than any other state including New York and California,” continued Zalman.

“Each year, Forbes judges the 100 largest banks in the United States on growth, credit quality, earnings, as well as other factors, for its America’s Best Banks list. Prosperity Bank has been ranked in the Top 10 since the list’s inception in 2010. We have twice been ranked number 1, were ranked number 2 in 2021 and are ranked number 6 for 2023. It is a testament to Prosperity’s performance, culture, vision and consistency and distinguishes us among most banks. I congratulate and thank all our customers, associates and directors for helping us achieve this honor,” stated Zalman.

“Prosperity has a talented team, deep bench, strong earnings, a solid capital position and a fortress balance sheet. We will continue working to help our customers and associates succeed and to build shareholder value,” concluded Zalman.

Results of Operations for the Three Months Ended March 31, 2023

Net income was $124.7 million(2) for the three months ended March 31, 2023 compared with $122.3 million(3) for the same period in 2022, an increase of $2.4 million or 1.9%. The change was primarily due to an increase in interest income from loans, securities and federal funds sold and other earning assets, partially offset by a decrease in SBA Paycheck Protection Program (“PPP”) loans fees and interest income of $3.6 million, a decrease in loan discount accretion of $4.3 million and an increase in interest expense. Net income per diluted common share was $1.37 for the three months ended March 31, 2023 compared with $1.33 for the same period in 2022, an increase of 3.0%. On a linked quarter basis, net income was $124.7 million(2) for the three months ended March 31, 2023 compared with $137.9 million(4) for the three months ended December 31, 2022. The change was primarily due to a decrease in net interest income. Net income per diluted common share was $1.37 for the three months ended March 31, 2023 compared with $1.51 for the three months ended December 31, 2022. Annualized returns on average assets, average common equity and average tangible common equity for the three months ended March 31, 2023 were 1.31%, 7.38% and 14.34%(1), respectively. Prosperity’s efficiency ratio (excluding net gains and losses on the sale or write down of assets and securities) was 43.68%(1) for the three months ended March 31, 2023.

Net interest income before provision for credit losses for the three months ended March 31, 2023 was $243.5 million compared with $239.9 million for the same period in 2022, an increase of $3.5 million or 1.5%. The change was primarily due to an increase in the average balances and average rates on loans held for investment and investment securities, partially offset by a decrease in PPP fees and interest income of $3.6 million, a decrease in loan discount accretion of $4.3 million, an increase in average borrowings and an increase in the average rates on interest-bearing deposits. On a linked quarter basis, net interest income before provision for credit losses was $243.5 million compared with $256.1 million for the three months ended December 31, 2022, a decrease of $12.7 million or 4.9%. The change was primarily due to an increase in the average balances and average rates on borrowings and an increase in average rates on interest-bearing deposits, partially offset by an increase in the average balances and average rates on loans held for investment and federal funds sold and other earning assets.

The net interest margin on a tax equivalent basis was 2.93% for the three months ended March 31, 2023 compared with 2.88% for the same period in 2022. The change was primarily due to an increase in the average balances and average rates on loans held for investment and investment securities and an increase in average rates on federal funds sold and other earnings assets, partially offset by a decrease in PPP fees and interest income of $3.6 million, a decrease in loan discount accretion of $4.3 million, an increase in average borrowings and an increase in the average rates on interest-bearing deposits. On a linked quarter basis, the net interest margin on a tax equivalent basis was 2.93% for the three months ended March 31, 2023 compared with 3.05% for the three months ended December 31, 2022. The change was primarily due to an increase in the average balances and average rates on borrowings and

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increase in average rates on interest-bearing deposits, partially offset by an increase in the average balances and average rates on loans held for investment and federal funds sold and other earning assets.

Noninterest income was $38.3 million for the three months ended March 31, 2023 compared with $35.1 million for the same period in 2022, an increase of $3.1 million or 9.0%. This change was primarily due to an increase in trust income and in other noninterest income. On a linked quarter basis, noninterest income was $38.3 million compared with $37.7 million for the three months ended December 31, 2022, an increase of $542 thousand or 1.4%.

Noninterest expense was $123.0 million for the three months ended March 31, 2023 compared with $119.9 million for the same period in 2022, an increase of $3.2 million or 2.6%. The change was primarily due to increases in regulatory assessments and FDIC insurance and merger related expenses, partially offset by a decrease in salaries and benefits. On a linked quarter basis, noninterest expense increased $3.8 million or 3.1% to $123.0 million compared with $119.2 million for the three months ended December 31, 2022. This change was primarily due to increases in salaries and benefits and regulatory assessments and FDIC insurance, partially offset by a decrease in other noninterest expense.

Balance Sheet Information

At March 31, 2023, Prosperity had $37.829 billion in total assets, a decrease of $442.0 million or 1.2%, compared with $38.271 billion at March 31, 2022.

Loans at March 31, 2023 were $19.334 billion, an increase of $494.5 million or 2.6% (10.5% annualized) from $18.840 billion at December 31, 2022, primarily due to increases in 1-4 family residential and commercial real estate loans. Loans increased $1.267 billion or 7.0%, compared with $18.068 billion at March 31, 2022, primarily due to increases in 1-4 family residential loans, and construction, land development and other land loans, partially offset by decreases in Warehouse Purchase Program loans and PPP loans. Loans, excluding Warehouse Purchase Program loans, at March 31, 2023 were $18.535 billion compared to $18.099 billion at December 31, 2022, an increase of $436.0 million or 2.4% (9.6% annualized), and compared to $16.723 billion at March 31, 2022, an increase of $1.812 billion or 10.8%.

Deposits at March 31, 2023 were $27.004 billion, a decrease of $1.529 billion or 5.4% compared with $28.534 billion at December 31, 2022 primarily due to a decrease in business demand deposits and public fund deposits. Deposits decreased $4.064 billion or 13.1%, compared with $31.068 billion at March 31, 2022, primarily due to a decrease in public fund deposits.

Asset Quality

Nonperforming assets totaled $24.5 million or 0.07% of quarterly average interest-earning assets at March 31, 2023 compared with $27.5 million or 0.08% of quarterly average interest-earning assets at December 31, 2022 and $27.2 million or 0.08% of quarterly average interest-earning assets at March 31, 2022 .

The allowance for credit losses on loans and off-balance sheet credit exposures was $312.1 million at March 31, 2023 compared with $311.5 million at December 31, 2022 and $315.1 million at March 31, 2022. There was no provision for credit losses for the three months ended March 31, 2023, December 31, 2022 and March 31, 2022.

The allowance for credit losses on loans was $282.2 million or 1.46% of total loans at March 31, 2023 compared with $281.6 million or 1.49% of total loans at December 31, 2022 and $285.2 million or 1.58% of total loans at March 31, 2022. Excluding Warehouse Purchase Program loans, the allowance for credit losses on loans to total loans was 1.52%(1) at March 31, 2023 compared with 1.56%(1) at December 31, 2022 and 1.71%(1) at March 31, 2022.

Net recoveries were $615 thousand for the three months ended March 31, 2023 compared with net charge-offs of $603 thousand for three months ended December 31, 2022 and net charge-offs of $1.2 million for the three months ended March 31, 2022. During the first quarter of 2023, net recoveries did not include any purchased credit deteriorated (“PCD”) loans and $241 thousand of specific reserves on resolved PCD loans was released to the general reserve.

Dividend

Prosperity Bancshares declared a second quarter 2023 cash dividend of $0.55 per share to be paid on July 3, 2023, to all shareholders of record as of June 15, 2023.

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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 611,263 shares of its common stock at an average weighted price of $62.20 per share during the three months ended March 31, 2023.

Pending Acquisition of First Bancshares of Texas, Inc.

On October 11, 2022, Prosperity Bancshares and First Bancshares of Texas, Inc. (“First Bancshares”) jointly announced the signing of a definitive merger agreement whereby First Bancshares, the parent company of FirstCapital Bank of Texas, N.A. (“FirstCapital Bank”) will merge with and into Prosperity. FirstCapital Bank operates 16 full-service banking offices in 6 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. As of March 31, 2023, First Bancshares, on a consolidated basis, reported total assets of $2.141 billion, total loans of $1.653 billion and total deposits of $1.712 billion.

Under the terms of the merger agreement, Prosperity will issue 3,583,370 shares of Prosperity common stock plus $93.4 million in cash for all outstanding shares of First Bancshares 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 $341.6 million. Prosperity has received all necessary regulatory approvals for the acquisition of First Bancshares, and the shareholders of First Bancshares approved the transaction on March 3, 2023. The transaction is expected to become effective on May 1, 2023, subject to customary closing conditions.

Pending Acquisition 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 March 31, 2023, Lone Star, on a consolidated basis, reported total assets of $1.383 billion, total loans of $1.032 billion and total deposits of $1.231 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 second quarter of 2023, although delays could occur.

Conference Call

Prosperity’s management team will host a conference call on Wednesday, April 26, 2023, at 11:30 a.m. Eastern Time (10:30 a.m. Central Time) to discuss Prosperity’s first 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 7001408.

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 home page by selecting “Presentations, Webcasts & Calls” from the menu on the Investor Relations link and following the instructions.

Non-GAAP Financial Measures

Prosperity’s management uses certain non-GAAP financial measures to evaluate its performance. Specifically, Prosperity reviews return on average tangible common equity; tangible book value per share; the tangible equity to tangible assets ratio; allowance for credit losses on loans to total loans excluding Warehouse Purchase Program loans; and the efficiency ratio excluding net gains and losses on the sale or write down of assets and securities, 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

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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 March 31, 2023, Prosperity Bancshares, Inc.® is a $37.829 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 272 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; 29 in the Central Texas area including Austin and San Antonio; 34 in the West Texas area including Lubbock, Midland-Odessa and Abilene; 16 in the Bryan/College Station area; 6 in the Central Oklahoma area; and 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 transactions with First Bancshares and 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, as well as expectations regarding the effects of the COVID-19 pandemic on Prosperity’s operating income, financial condition and cash flows. 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 First Bancshares and 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 the anticipated benefits of an acquisition transaction, including the pending transactions with First Bancshares and 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

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commodity price fluctuations; the effect, impact, potential duration or other implications of the COVID-19 pandemic; and weather. 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 $(4,399), $(4,396), $(296), $1,517 and $2,115 in unrealized (losses) gains on available for sale securities for the quarterly periods ended March 31, 2023, December 31, 2022, September 30, 2022, June 30, 2022 and March 31, 2022, respectively.

(B) Includes $(3,476), $(3,473), $(234), $1,198 and $1,671 in after-tax unrealized (losses) gains on available for sale securities for the quarterly periods ended March 31, 2023, December 31, 2022, September 30, 2022, June 30, 2022 and March 31, 2022, respectively.

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Prosperity Bancshares, Inc.®

Financial Highlights (Unaudited)

(In thousands)

(C) Interest income on securities was reduced by net premium amortization of $7,384, $8,703, $9,947, $11,450 and $12,857 for the three months ended March 31, 2023, December 31, 2022, September 30, 2022, June 30, 2022 and March 31, 2022, respectively.

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Prosperity Bancshares, Inc. ®

Financial Highlights (Unaudited)

(Dollars and share amounts in thousands, except per share data and market prices)