=== SEC Form 4 — Statement of Changes in Beneficial Ownership ===
Document Type: 4
Period of Report: 2026-05-18
10b5-1 Pre-arranged Plan: No
--- 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: 2026-05-18 | Code: S (Open market sale)
Shares: -3,424 | Price: $1,462.61
Total Value: $5,007,976.64
Shares Owned After: 884,839 | Ownership: D (Direct)
Footnotes:
[F2] 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 $1,459.96 to $1,464.86. 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.
[F1] Ending balance includes 29 shares acquired on February 17, 2026 through the Company's qualified ESPP program.
[Transaction #2]
Security: Common Stock
Date: 2026-05-18 | Code: S (Open market sale)
Shares: -5,819 | Price: $1,467.62
Total Value: $8,540,080.78
Shares Owned After: 879,020 | Ownership: D (Direct)
Footnotes:
[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 $1,464.97 to $1,469.94. 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: 2026-05-18 | Code: S (Open market sale)
Shares: -5,049 | Price: $1,472.84
Total Value: $7,436,369.16
Shares Owned After: 873,971 | Ownership: D (Direct)
Footnotes:
[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 $1,469.95 to $1,474.94. 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: 2026-05-18 | Code: S (Open market sale)
Shares: -4,082 | Price: $1,476.96
Total Value: $6,028,950.72
Shares Owned After: 869,889 | Ownership: D (Direct)
Footnotes:
[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 $1,474.95 to $1,479.85. 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: 2026-05-18 | Code: S (Open market sale)
Shares: -5,737 | Price: $1,482.51
Total Value: $8,505,159.87
Shares Owned After: 864,152 | Ownership: D (Direct)
Footnotes:
[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 $1,479.99 to $1,484.93. 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: 2026-05-18 | Code: S (Open market sale)
Shares: -6,688 | Price: $1,486.76
Total Value: $9,943,450.88
Shares Owned After: 857,464 | Ownership: D (Direct)
Footnotes:
[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 $1,484.95 to $1,489.73. 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: 2026-05-18 | Code: S (Open market sale)
Shares: -862 | Price: $1,491.48
Total Value: $1,285,655.76
Shares Owned After: 856,602 | Ownership: D (Direct)
Footnotes:
[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 $1,490.17 to $1,494.10. 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: 2026-05-18 | Code: S (Open market sale)
Shares: -608 | Price: $1,499.46
Total Value: $911,671.68
Shares Owned After: 855,994 | Ownership: D (Direct)
Footnotes:
[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 $,1495.74 to $1,500.72. 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 #9]
Security: Common Stock
Date: 2026-05-18 | Code: S (Open market sale)
Shares: -2,929 | Price: $1,503.05
Total Value: $4,402,433.45
Shares Owned After: 853,065 | Ownership: D (Direct)
Footnotes:
[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 $1,500.75 to $1,505.70. 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 #10]
Security: Common Stock
Date: 2026-05-18 | Code: S (Open market sale)
Shares: -3,769 | Price: $1,507.70
Total Value: $5,682,521.30
Shares Owned After: 849,296 | Ownership: D (Direct)
Footnotes:
[F11] 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 $1,505.70 to $1,510.67. 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 #11]
Security: Common Stock
Date: 2026-05-18 | Code: S (Open market sale)
Shares: -551 | Price: $1,513.11
Total Value: $833,723.61
Shares Owned After: 848,745 | Ownership: D (Direct)
Footnotes:
[F12] 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 $1,510.68 to $1,515.44. 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 #12]
Security: Common Stock
Date: 2026-05-18 | Code: S (Open market sale)
Shares: -352 | Price: $1,518.15
Total Value: $534,388.80
Shares Owned After: 848,393 | Ownership: D (Direct)
Footnotes:
[F13] 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 $1,516.26 to $1,519.25. 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 #13]
Security: Common Stock
Date: 2026-05-18 | Code: S (Open market sale)
Shares: -130 | Price: $1,521.43
Total Value: $197,785.90
Shares Owned After: 848,263 | Ownership: D (Direct)
Footnotes:
[F14] 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 $1,521.33 to $1,521.56. 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: Ending balance includes 29 shares acquired on February 17, 2026 through the Company's qualified ESPP program.
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 $1,500.75 to $1,505.70. 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.
F11: 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 $1,505.70 to $1,510.67. 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.
F12: 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 $1,510.68 to $1,515.44. 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.
F13: 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 $1,516.26 to $1,519.25. 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.
F14: 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 $1,521.33 to $1,521.56. 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: 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 $1,459.96 to $1,464.86. 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.
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 $1,464.97 to $1,469.94. 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 $1,469.95 to $1,474.94. 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 $1,474.95 to $1,479.85. 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 $1,479.99 to $1,484.93. 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 $1,484.95 to $1,489.73. 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 $1,490.17 to $1,494.10. 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 $,1495.74 to $1,500.72. 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 (2026-05-20)
