As filed with the Securities and Exchange Commission on February 4, 2021

            Registration No. 333-                

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

ALLEGRO MICROSYSTEMS, INC.

(Exact name of registrant as specified in its charter)

955 Perimeter Road

Manchester, New Hampshire 03103

Telephone: (603) 626-2300

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Ravi Vig

Chief Executive Officer

Allegro MicroSystems, Inc.

955 Perimeter Road

Manchester, New Hampshire 03103

Telephone: (603) 626-2300

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies of all communications, including communications sent to agent for service, should be sent to:

Approximate date of commencement of proposed sale to the public:

As soon as practicable after this Registration Statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box.  ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☒ File No. 333-252667

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a 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.

If an emerging growth company, indicate by checkmark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided to Section 7(a)(2)(B) of the Securities Act.  ☐

CALCULATION OF REGISTRATION FEE

This Registration Statement shall become effective upon filing with the Securities and Exchange Commission in accordance with Rule 462(b) promulgated under the Securities Act.

EXPLANATORY NOTE AND INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

This Registration Statement is being filed with the Securities and Exchange Commission (the “Commission”) pursuant to Rule 462(b) under the Securities Act of 1933, as amended. This Registration Statement relates to the public offering of common stock, par value $0.01 per share, of the Registrant contemplated by the Registration Statement on Form S-1 (File No. 333-252667) (as amended, the “Prior Registration Statement”), which the Commission declared effective on February 4, 2021. The contents of the Prior Registration Statement, including all exhibits thereto, are incorporated by reference into this Registration Statement.

The Registrant is filing this Registration Statement for the sole purpose of increasing the aggregate number of shares of common stock offered by the Registrant by 2,875,000 shares of its common stock, which includes 375,000 shares of common stock that may be sold pursuant to the underwriters’ option to purchase additional shares. The additional shares of common stock that are being registered for issuance and sale are in an amount and at a price that together represent no more than 20% of the maximum aggregate offering price set forth in the Calculation of Registration Fee table contained in the Prior Registration Statement.

The required opinion and consents are listed in Part II, Item 16 of this Registration Statement and filed herewith.

PART II

Information Not Required in Prospectus

The following documents are filed as exhibits to this Registration Statement, and all other exhibits previously filed as exhibits to the Registrant’s Registration Statement on Form S-1, (File No. 333-252667), are incorporated by reference into, and shall be deemed to be a part of, this filing.

i-1

SIGNATURES

Pursuant to the requirements of the Securities Act, Allegro MicroSystems, Inc. has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in Manchester, New Hampshire, on this 4^th day of February, 2021.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed by the following persons in the capacities held on the dates indicated.