Monolithic Power Systems' Hsing proposes $40.3M sale

The shares came from performance-share vesting and Employee Stock Purchase Plan purchases dated from 2023 through 2025.

Rhea-AI Filing Summary

Monolithic Power Systems, Inc. officer and director Michael Hsing reported a proposed sale of 30,000 common shares, with an aggregate market value of $40,349,049.00 and an approximate sale date of September 28, 2026. The shares comprise 29,961 performance shares and 39 Employee Stock Purchase Plan shares; the remarks describe their acquisition periods as spanning 2023 through 2025.

Key Figures

Common shares proposed for sale: 30,000 shares Aggregate market value: $40,349,049.00 Shares outstanding: 49,143,000 shares +2 more

5 metrics

Common shares proposed for sale 30,000 shares Approximate sale date: September 28, 2026

Aggregate market value $40,349,049.00 Proposed sale

Shares outstanding 49,143,000 shares Issuer shares outstanding as listed

Performance shares 29,961 shares Shares listed for sale; acquired upon vesting

Employee Stock Purchase Plan shares 39 shares Shares listed for sale; acquired through purchases

Key Terms

Performance Shares, Employee Stock Purchase Plan, Rule 144

3 terms

Performance Shares financial

"acquired upon the vesting of Performance Shares"

Performance shares are a type of company stock given to executives or employees that only become theirs if the company meets specific goals, like hitting certain profits or growth targets. They motivate leaders to work toward the company’s success, because their additional shares depend on achieving these results.

Employee Stock Purchase Plan financial

"Employee Stock Purchase Plan shares"

An employee stock purchase plan is a company program that lets workers buy shares through small payroll deductions, often at a discount to the market price and after a set offering period. Think of it like a workplace savings plan that turns into ownership: it encourages employees to share in the company’s success and can create predictable buying or selling of stock that investors watch because it affects supply, demand and employee incentives.

Rule 144 regulatory

"definition of "person" in paragraph (a) of Rule 144"

Rule 144 is a U.S. securities regulation that sets conditions under which restricted or insider-held shares can be legally resold to the public, such as required holding periods, availability of public information, limits on how much can be sold at once, and certain filing requirements. For investors it matters because it determines when previously locked-up shares can enter the market — like a release valve that can increase supply, affect share price, and signal insider intent.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many MPWR shares does Michael Hsing plan to sell?

Michael Hsing's proposed sale is for 30,000 common shares, with an approximate sale date of September 28, 2026.

How did Michael Hsing acquire the MPWR shares listed for sale?

The remarks state that 29,961 performance shares were acquired upon vesting from June 30, 2023, through February 7, 2025, and that 39 Employee Stock Purchase Plan shares were purchased from February 15, 2023, through February 17, 2025.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 09/28/2026 - 05:51 PM Accepted by SEC EDGAR 09/28/2026 - 05:50 PM Learn about SEC filing dates

Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0001308676
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	MONOLITHIC POWER SYSTEMS, INC.
SEC File Number	000-51026
Address of Issuer	1555 Palm Beach Lakes Blvd. West Palm Beach FLORIDA 33401
Phone	(561) 839-3999
Name of Person for Whose Account the Securities are To Be Sold	MICHAEL HSING
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Officer
Relationship to Issuer	Director

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Common	Morgan Stanley Smith Barney LLC Executive Financial Services 1 New York Plaza 8th Floor New York NY 10004	30000	40349049.00	49143000	09/28/2026	NASDAQ

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Common	06/30/2023	Performance Shares	ISSUER			29961	06/30/2023	Not Applicable
Common	02/15/2023	Employee Stock Purchase Plan	ISSUER			39	02/15/2023	Cash

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Nothing to Report

144: Remarks and Signature

Remarks	The securities to be sold were acquired upon the vesting of Performance Shares during the period of 06/30/2023 through 02/07/2025 The securities to be sold were acquired upon the purchase of Employee Stock Purchase Plan shares during the period of 02/15/2023 through 02/17/2025
Date of Notice	09/28/2026
Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1	05/29/2026
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ Michael Hsing
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)