BlackRock unit discloses 8.2% Masimo (MASI) ownership stake

Rhea-AI Filing Summary

BlackRock Portfolio Management LLC filed an amended Schedule 13G reporting its beneficial ownership of MASIMO CORPORATION common stock as of 12/31/2025. The firm reports beneficial ownership of 4,386,302 shares of common stock, representing 8.2% of the outstanding class. It has sole power to vote 4,290,570 shares and sole power to dispose of 4,386,302 shares, with no shared voting or dispositive power.

The filing explains that the shares are held by certain business units of BlackRock, Inc. and affiliates, and that various underlying persons have rights to dividends or sale proceeds, but no single person has more than five percent of the total outstanding common shares. BlackRock Portfolio Management LLC certifies that the securities were acquired and are held in the ordinary course of business and not for the purpose of changing or influencing control of Masimo.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

MASIMO CORPORATION

(Name of Issuer)

Common Stock

(Title of Class of Securities)

574795100

(CUSIP Number)

12/31/2025

(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)

SCHEDULE 13G

CUSIP No. 574795100

1

Names of Reporting Persons

BlackRock Portfolio Management 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 4,290,570.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 4,386,302.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,386,302.00

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)

8.2 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

Item 1.
(a)	Name of issuer: MASIMO CORPORATION
(b)	Address of issuer's principal executive offices: 52 DISCOVERY IRVINE CA 92618
Item 2.
(a)	Name of person filing: BlackRock Portfolio Management LLC In accordance with SEC Release No. 34-39538 (January 12, 1998), this Schedule 13G reflects the securities beneficially owned, or deemed to be beneficially owned, by certain business units (collectively, the "Reporting Business Units") of BlackRock, Inc. and its subsidiaries and affiliates. It does not include securities, if any, beneficially owned by other business units whose beneficial ownership of securities are disaggregated from that of the Reporting Business Units in accordance with such release.
(b)	Address or principal business office or, if none, residence: BlackRock Portfolio Management LLC, 50 Hudson Yards New York, NY 10001
(c)	Citizenship: See Item 4 of Cover Page
(d)	Title of class of securities: Common Stock
(e)	CUSIP No.: 574795100
Item 4.	Ownership
(a)	Amount beneficially owned: 4386302
(b)	Percent of class: 8.2 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 4290570
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 4386302
	(iv) Shared power to dispose or to direct the disposition of: 0
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. Various persons 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 MASIMO CORPORATION. No one person's interest in the common stock of MASIMO CORPORATION is more than five percent of the total outstanding common shares.
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 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.

BlackRock Portfolio Management LLC

Signature:	Spencer Fleming
Name/Title:	Managing Director
Date:	01/21/2026

Exhibit Information

Exhibit 24: Power of Attorney Exhibit 99: Item 7

FAQ

How many Masimo (MASI) shares does BlackRock Portfolio Management LLC report owning?

BlackRock Portfolio Management LLC reports beneficial ownership of 4,386,302 MASIMO CORPORATION common shares, with sole dispositive power over that amount.

What percentage of Masimo’s common stock does BlackRock Portfolio Management LLC own?

The filing states that BlackRock Portfolio Management LLC beneficially owns 8.2% of MASIMO CORPORATION’s common stock as of 12/31/2025.

Does BlackRock Portfolio Management LLC have voting control over its Masimo shares?

The firm has sole voting power over 4,290,570 Masimo shares and reports no shared voting power and no shared dispositive power.

Is BlackRock Portfolio Management LLC a passive investor in Masimo (MASI)?

Yes. The certification states the Masimo securities were acquired and are held in the ordinary course of business and not for the purpose of changing or influencing control of the issuer.

Do any underlying investors hold more than 5% of Masimo through BlackRock?

The filing notes that various persons may receive dividends or sale proceeds, but no one person’s interest exceeds five percent of Masimo’s total outstanding common shares.

Who signed the Schedule 13G/A for BlackRock Portfolio Management LLC?

The statement was signed by Spencer Fleming, Managing Director of BlackRock Portfolio Management LLC, dated 01/21/2026.