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FMR LLC and Abigail P. Johnson reported beneficial ownership of 9,913,111.69 shares of Allegro Microsystems, Inc. (ALGM) common stock, equal to 5.3% of the class, as of September 30, 2026. FMR LLC reported sole voting power over 9,879,971.02 shares and sole dispositive power over 9,913,111.69 shares; Abigail P. Johnson reported sole dispositive power over 9,913,111.69 shares and 0.00 sole voting power.
Key Figures
Beneficial ownership:9,913,111.69 sharesPercent of class:5.3%Sole voting power:9,879,971.02 shares+2 more
5 metrics
Beneficial ownership9,913,111.69 sharesFMR LLC and Abigail P. Johnson; as of September 30, 2026
Percent of class5.3%Beneficial ownership reported as of September 30, 2026
Sole voting power9,879,971.02 sharesFMR LLC
Sole dispositive power9,913,111.69 sharesFMR LLC
Sole voting power0.00 sharesAbigail P. Johnson
Key Terms
beneficially owned, Sole Voting Power, Sole Dispositive Power
3 terms
beneficially ownedfinancial
"Amount beneficially owned"
Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.
Sole Voting Powerfinancial
"Sole Voting Power 9,879,971.02"
Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.
Sole Dispositive Powerfinancial
"Sole Dispositive Power 9,913,111.69"
Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.
FAQ
AI-generated questions and answers. How Rhea-AI works. Not financial advice.
How many ALGM shares did FMR LLC report beneficially owning?
FMR LLC reported beneficial ownership of 9,913,111.69 shares, equal to 5.3% of the class, as of September 30, 2026.
Did any other person have an interest in more than 5% of ALGM?
FMR LLC stated that one or more other persons were known to have rights to dividends from, or proceeds from sales of, the common stock, but no one other person's interest was more than 5% of the total outstanding common stock.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
(Amendment No. 8)
ALLEGRO MICROSYSTEMS INC
(Name of Issuer)
COMMON STOCK
(Title of Class of Securities)
01749D105
(CUSIP Number)
09/30/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
01749D105
1
Names of Reporting Persons
FMR LLC
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
9,879,971.02
6
Shared Voting Power
0.00
7
Sole Dispositive Power
9,913,111.69
8
Shared Dispositive Power
0.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
9,913,111.69
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
5.3 %
12
Type of Reporting Person (See Instructions)
HC
SCHEDULE 13G
CUSIP Number(s):
01749D105
1
Names of Reporting Persons
Abigail P. Johnson
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
0.00
7
Sole Dispositive Power
9,913,111.69
8
Shared Dispositive Power
0.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
9,913,111.69
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
5.3 %
12
Type of Reporting Person (See Instructions)
IN
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
ALLEGRO MICROSYSTEMS INC
(b)
Address of issuer's principal executive offices:
955 PERIMETER ROAD,MANCHESTER,NH,USA,03103
Item 2.
(a)
Name of person filing:
FMR LLC
(b)
Address or principal business office or, if none, residence:
245 Summer Street, Boston, Massachusetts 02210
(c)
Citizenship:
Not applicable
(d)
Title of class of securities:
COMMON STOCK
(e)
CUSIP No.:
01749D105
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
9913111.69
(b)
Percent of class:
5.3 %
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
Please see the responses to Items 5 and 6 on the cover page.
(ii) Shared power to vote or to direct the vote:
0.00
(iii) Sole power to dispose or to direct the disposition of:
9913111.69
(iv) Shared power to dispose or to direct the disposition of:
0.00
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required.
One or more other persons are known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the COMMON STOCK of ALLEGRO MICROSYSTEMS INC. No one other person's interest in the COMMON STOCK of ALLEGRO MICROSYSTEMS INC is more than five percent of the total outstanding COMMON STOCK.
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary.
See attached Exhibit 99.
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
FMR LLC
Signature:
Stephanie J. Brown
Name/Title:
Duly authorized under Power of Attorney effective as of January 3, 2023, by and on behalf of FMR LLC and its direct and indirect subsidiaries*
Date:
10/06/2026
Abigail P. Johnson
Signature:
Stephanie J. Brown
Name/Title:
Duly authorized under Power of Attorney effective as of January 26, 2023, by and on behalf of Abigail P. Johnson**
Date:
10/06/2026
Comments accompanying signature: * This power of attorney is incorporated herein by reference to Exhibit 24 to the Schedule 13G filed by FMR LLC on January 10, 2023, accession number: 0000315066-23-000003.
** This power of attorney is incorporated herein by reference to Exhibit 24 to the Schedule 13G filed by FMR LLC on January 31, 2023, accession number: 0000315066-23-000038.
