FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * Tseng Saria   2. Issuer Name and Ticker or Trading Symbol MONOLITHIC POWER SYSTEMS INC [MPWR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) VP & General Counsel (Last) (First) (Middle) 79 GREAT OAKS BLVD 3. Date of Earliest Transaction (Month/Day/Year) 02/03/2015 (Street) SAN JOSE, CA 95119 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 02/03/2015   A   90,181 (1) A $ 0 206,346 D   Common Stock 02/03/2015   S(2)   1,013 D $ 47.21 205,333 D   Common Stock 02/03/2015   S(2)   51 D $ 47.21 205,282 D   Common Stock 02/03/2015   A   8,071 (3) A $ 0 213,353 D   Common Stock 02/05/2015   S   724 (2) D $ 48.0202 212,629 D   Common Stock 02/05/2015   S   6,090 (2) D $ 47.7955 206,539 D   Common Stock 02/05/2015   S   15,127 (2) D $ 47.7954 191,412 D   Common Stock               2,000 I S.Tseng Charity Fund

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Tseng Saria 79 GREAT OAKS BLVD SAN JOSE, CA 95119			VP & General Counsel

Signatures

By: Saria Tseng For: Saria Tseng		02/05/2015
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	On February 11, 2013, the reporting person was granted a target of 31,930 shares of restricted stock units subject to satisfaction of pre-determined, performance-based vesting criteria. On February 3, 2015, the Company's Board of Directors determined that those performance criteria for the restricted stock units had been satisfied, which resulted in 58,251 additional shares being achieved and granted to the reporting person. Of the restricted stock units that were awarded, 45,090 will vest immediately and 45,091 will vest quarterly in the next two years.
(2)	Shares sold to pay tax obligations resulting from the vesting of restricted stock units.
(3)	1/12 of the Restricted Stock Units shall vest quarterly following the Vesting Commencement Date, provided that the Grantee continues to be a Service Provider from the Grant Date through each applicable vesting date.

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