SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP 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	OMB APPROVAL OMB Number: 3235-0287 Expires: February 28, 2011 Estimated average burden hours per response 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* VOICU GELU (Last) (First) (Middle) 5005 EAST MCDOWELL ROAD (Street) PHOENIX AZ 85008 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol ON SEMICONDUCTOR CORP [ ONNN ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director 10% Owner X Officer (give title below) Other (specify below) SVP, Catalyst Group
	3. Date of Earliest Transaction (Month/Day/Year) 10/10/2008
	4. If Amendment, Date of 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

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	10/10/2008		A		319,829 ( 1 )	A	$0	344,829	D

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 Securities Underlying Derivative Security (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: 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
Stock Option (right to buy)	$2.46	10/10/2008		A		43,804 ( 2 )		10/10/2008	09/27/2011	Common	43,804	$0	43,804	D
Stock Option (right to buy)	$3.25	10/10/2008		A		155,319 ( 3 )		10/10/2008	10/10/2011	Common	155,319	$0	155,319	D
Stock Option (right to buy)	$3.25	10/10/2008		A		56,480 ( 4 )		10/10/2008	10/10/2011	Common	56,480	$0	211,799	D
Stock Option (right to buy)	$3.32	10/10/2008		A		141,200 ( 5 )		10/10/2008	10/10/2011	Common	141,200	$0	141,200	D
Stock Option (right to buy)	$4.52	10/10/2008		A		100,004 ( 6 )		10/10/2009	10/10/2018	Common	100,004	$0	100,004	D
Stock Option (right to buy)	$4.75	10/10/2008		A		70,600 ( 7 )		10/10/2008	10/10/2011	Common	70,600	$0	70,600	D
Stock Option (right to buy)	$4.75	10/10/2008		A		26,475 ( 8 )		10/10/2008	10/10/2011	Common	26,475	$0	97,075	D
Stock Option (right to buy)	$4.75	10/10/2008		A		13,237 ( 9 )		10/10/2008	10/10/2011	Common	13,237	$0	110,312	D
Stock Option (right to buy)	$4.75	10/10/2008		A		13,237 ( 10 )		10/10/2008	10/10/2011	Common	13,237	$0	123,549	D
Stock Option (right to buy)	$5.97	10/10/2008		A		141,200 ( 11 )		10/10/2008	10/10/2011	Common	141,200	$0	141,200	D
Stock Option (right to buy)	$6.05	10/10/2008		A		96,365 ( 12 )		10/10/2008	10/10/2011	Common	96,365	$0	96,365	D
Stock Option (right to buy)	$6.05	10/10/2008		A		44,834 ( 13 )		10/10/2008	10/10/2011	Common	44,834	$0	141,199	D

Explanation of Responses:

1. Received, in part, a total of 319,829 (202,386 shares of common stock and 117,433 restricted stock units ("RSUs")) of ON Semiconductor Corporation (Issuer) plus cash representing fractional shares as provided in the merger agreement in exchange for a total of 453,017 (286,667 shares of common stock and 166,350 RSUs) of Catalyst Semiconductor, Inc. ("CATALYST") in connection with the merger of CATALYST in to the Issuer ("Merger"). The Merger was effective on October 10, 2008. Pursuant to the Merger, each outstanding share of CATALYST common stock and/or right thereto was converted in to the right to receive .706 shares of the Issuer's common stock. The exchanged RSUs are, among other things, subject to the Issuer's 2000 Stock Incentive Plan ("Plan"), a previous grant agreement, vesting over time (generally), and a conversion and assumption by the Issuer.

2. Received in the Merger in exchange for an employee stock option to acquire 62,046 shares of CATALYST for $1.73 per share. The exchanged options accelerated and vested immediately the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

3. Received in the Merger in exchange for an employee stock option to acquire 219,999 shares of CATALYST for $2.29 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

4. Received in the Merger in exchange for an employee stock option to acquire 80,001 shares of CATALYST for $2.29 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

5. Received in the Merger in exchange for an employee stock option to acquire 200,000 shares of CATALYST for $2.34 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

6. Received in the Merger in exchange for an employee stock option to acquire 141,650 shares of CATALYST for $3.19 per share. Generally, the grant provides for pro rata vesting of 25% per year for each of the first through fourth anniversaries of the grant date. The exchanged options, are among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

7. Received in the Merger in exchange for an employee stock option to acquire 100,000 shares of CATALYST for $3.35 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

8. Received in the Merger in exchange for an employee stock option to acquire 37,500 shares of CATALYST for $3.35 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

9. Received in the Merger in exchange for an employee stock option to acquire 18,750 shares of CATALYST for $3.35 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

10. Received in the Merger in exchange for an employee stock option to acquire 18,750 shares of CATALYST for $3.35 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

11. Received in the Merger in exchange for an employee stock option to acquire 200,000 shares of CATALYST for $4.21 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

12. Received in the Merger in exchange for an employee stock option to acquire 136,495 shares of CATALYST for $4.27 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

13. Received in the Merger in exchange for an employee stock option to acquire 63,505 shares of CATALYST for $4.27 per share. The exchanged options accelerated and vested immediately on the closing date of the Merger. The exchanged options are, among other things, subject to the Plan, a previous grant agreement, and a conversion and assumption by the Issuer.

Remarks:

Judith A. Boyle is signing on behalf of the Reporting Person pursuant to a Power of Attorney attached herein as an exhibit. poavoicu.TXT

	Judith A. Boyle, Attorney-in-Fact	10/15/2008
	** Signature of Reporting Person	Date
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