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Proxy Statement Pursuant to

Section 14(a) of the Securities Exchange Act of 1934

(Amendment No.)


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Preliminary Proxy Statement

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Definitive Proxy Statement

Definitive Additional Materials

Soliciting Material under §240.14a-12

Allegro MicroSystems, Inc.

(Name of Registrant as Specified in its Charter)

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Allegro Microsystems innovation with purpose vote Online Go to or scan the QR code — login details are located in the shaded bar below. Shareholder meeting notice Important Notice Regarding the Availability of Proxy Materials for the Allegro MicroSystems, Inc. Annual Meeting of Shareholders to be Held on August 8, 2024. Under Securities and Exchange Commission rules, you are receiving this notice that the proxy materials for the annual meeting of shareholders are available on the Internet. Follow the instructions below to view the materials and vote online or request a copy. The items to be voted on and location of the annual meeting are on the reverse side. Your vote is important! This communication presents only an overview of the more complete proxy materials that are available to you on the Internet or by mail. We encourage you to access and review all of the important information contained in the proxy materials before voting. The 2024 Notice and Proxy Statement and Fiscal 2024 Annual Report to Shareholders are available at: Easy Online Access — View your proxy materials and vote. Step 1: Go to Step 2: Click on Cast Your Vote or Request Materials. Step 3: Follow the instructions on the screen to log in. Step 4: Make your selections as instructed on each screen for your delivery preferences. Step 5: Vote your shares. When you go online, you can also help the environment by consenting to receive electronic delivery of future materials. Obtaining a Copy of the Proxy Materials – If you want to receive a paper or email copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. Please make your request as instructed on the reverse side on or before July 29, 2024 to facilitate timely delivery. 03ZXKB 2 N O T + Meeting NoticeThe 2024 Annual Meeting of Shareholders of Allegro MicroSystems, Inc. will be held on Thursday, August 8, 2024, at 8:30 a.m., Eastern Time, virtually via the Internet at To access the virtual meeting,participate and vote online during the meeting, you must have the information that is printed in the shaded bar located on the reverse side of this form.Proposals to be voted on at the meeting are listed below along with the Board of Directors’ recommendations. The Board of Directors recommends a vote FOR all the nominees listed, and FOR Proposals 2 and 3. 1. To elect four individuals to the Board of Directors for three-year terms expiring in 2027: 01 – Katsumi Kawashima 02 – Joseph R. Martin 03 – VineetNargolwala 04 – Mary G. Puma 2. To ratify the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the fiscal year ending March 28, 2025. 3. To approve,on an advisory basis, the Company’s executivecompensation. PLEASE NOTE – YOU CANNOT VOTE BY RETURNINGTHIS NOTICE. To vote your shares you must vote online, by phone, or request a paper copy of the proxy materials to receive a proxy card that you must sign and return following the instructions on the proxycard. Here’s how to order a paper or email copy of the proxy materials and select delivery preferences: Current and