=== SEC Form 4 — Statement of Changes in Beneficial Ownership ===
Document Type: 4
Period of Report: 2026-09-28
10b5-1 Pre-arranged Plan: Yes
--- Issuer ---
Name: MONOLITHIC POWER SYSTEMS, INC. (MPWR)
CIK: 0001280452
--- Reporting Owner ---
Name: Hsing Michael
CIK: 0001308676
Role: Director, Officer (CEO)
--- Non-Derivative Transactions ---
[Transaction #1]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -596 | Price: $1,323.31
Total Value: $788,692.76
Shares Owned After: 847,668 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F3] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,320.64 to $1,325.61. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[F2] Ending balance includes 1 share acquired on August 17, 2026, through the Company's qualified ESPP program.
[Transaction #2]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -2,121 | Price: $1,328.54
Total Value: $2,817,833.34
Shares Owned After: 845,547 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F4] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,325.65 to $1,330.62. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #3]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -1,111 | Price: $1,333.34
Total Value: $1,481,340.74
Shares Owned After: 844,436 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F5] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,330.65 to $1,335.51. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #4]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -2,949 | Price: $1,338.66
Total Value: $3,947,708.34
Shares Owned After: 841,487 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F6] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,335.68 to $1,340.66. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #5]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -5,783 | Price: $1,343.76
Total Value: $7,770,964.08
Shares Owned After: 835,704 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F7] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,340.69 to $1,345.65. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #6]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -6,343 | Price: $1,347.15
Total Value: $8,544,972.45
Shares Owned After: 829,361 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F8] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,345.66 to $1,350.47. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #7]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -10,967 | Price: $1,351.43
Total Value: $14,821,132.81
Shares Owned After: 818,394 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F9] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,350.84 to $1,355.11. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #8]
Security: Common Stock
Date: 2026-09-28 | Code: S (Open market sale)
Shares: -130 | Price: $1,356.94
Total Value: $176,402.20
Shares Owned After: 818,264 | Ownership: D (Direct)
Footnotes:
[F1] These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
[F10] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,356.78 to $1,357.00. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
--- Holdings ---
[Holding #1]
Security: Common Stock
Ownership: I (Indirect)
[Holding #2]
Security: Common Stock
Ownership: I (Indirect)
--- Footnotes (Complete Index) ---
F1: These transactions were made pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on 05/29/2026.
F10: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,356.78 to $1,357.00. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F2: Ending balance includes 1 share acquired on August 17, 2026, through the Company's qualified ESPP program.
F3: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,320.64 to $1,325.61. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F4: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,325.65 to $1,330.62. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F5: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,330.65 to $1,335.51. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F6: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,335.68 to $1,340.66. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F7: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,340.69 to $1,345.65. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F8: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,345.66 to $1,350.47. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F9: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,350.84 to $1,355.11. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
--- Signature ---
/s/ /s/ Saria Tseng, attorney-in-fact for Mr. Michael R. Hsing (2026-09-30)
