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) 02/07/2013 (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 02/07/2013   M(1)   16,250 A $ 13.01 90,514 D   Common Stock 02/07/2013   M(1)   16,250 D $ 24.4683 (2) 74,264 D   Common Stock 02/07/2013   M(1)   9,001 A $ 8 83,265 D   Common Stock 02/07/2013   S(1)   9,001 D $ 24.5899 (3) 74,264 D   Common Stock 02/07/2013   A(4)   151 A $ 0 74,415 D   Common Stock 02/11/2013   S(5)   1,207 D $ 24.6 73,208 D   Common Stock 02/11/2013   S(5)   58 D $ 24.6 73,150 D   Common Stock               3,000 I S.Tseng Charity Fund

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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

Non-Qualified Stock Option (right to buy)

$ 8

02/07/2013

M(1)

9,001

10/15/2005

11/17/2014

Common Stock

9,001

$ 0

10,000

D

Non-Qualified Stock Option (right to buy)

$ 13.01

02/07/2013

M

16,250

10/22/2010(1)

10/22/2015

Common Stock

16,250

$ 0

3,750

D

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: Meera Rao For: Saria Tseng		02/11/2013
**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)	In accordance with the reporting person's 10b5-1 trading plan.
(2)	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 $24.19 to $24.99. 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.
(3)	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 $24.43 to $24.92. 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.
(4)	Equitable stock dividend adjustment approved by the Board of Director as a result of dividend Payment to shareholders on December 28, 2012. Stock dividends will release according to the same vesting schedule as the original grants.
(5)	Shares sold to pay tax obligations resulting from the release of restricted stock units.

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