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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , DC 20549 FORM 10 - K ( Mark One ) ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended March 26 , 2021 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Commission File Number : 001-39675 Delaware ( State or other jurisdiction of incorporation or organization ) ALLEGRO MICROSYSTEMS , INC . ( Exact Name of Registrant as Specified in its Charter ) to 955 Perimeter Road Manchester , New Hampshire ( Address of principal executive offices ) Large accelerated filer Non - accelerated filer 46-2405937 ( I.R.S. Employer Identification No. ) 03103 ( Zip Code ) ( 603 ) 626-2300 ( Registrant's telephone number , including area code ) N / A ( Former name , former address and former fiscal year , if changed since last report ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) ALGM Title of each class Common Stock , par value $ 0.01 per share Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes Indicate by check mark whether the registrant : ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No No X No X Name of each exchange on which registered The Nasdaq Global Select Market Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No ☐ Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Accelerated filer Smaller reporting company Emerging growth company DOCUMENTS INCORPORATED BY REFERENCE □□ If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No X The Registrant was not a public company as of the last business day of its most recently completed second fiscal quarter , and therefore , cannot calculate the aggregate market value of the voting and non - voting common equity held by non - affiliates as of such date . As of May 10 , 2021 , the aggregate market value of the registrant's common stock held by non - affiliates of the registrant was approximately $ 1.3 billion based upon the closing sale price of the common stock on that date on the Nasdaq Global Select Market . As of May 10 , 2021 , the registrant had 189,593,243 shares of common stock , $ 0.01 par value per share , outstanding .