As filed with the U.S. Securities and Exchange Commission on January 15, 2015

                            File Nos. 333-179904 and 811-22649                                                                                

 UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933	x
Post-Effective Amendment No. 138	x
and/or
REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940	x
Amendment No. 138	x

(Check appropriate box or boxes)

iShares U.S. ETF Trust

(Exact Name of Registrant as Specified in Charter)

c/o State Street Bank and Trust Company

1 Iron Street

Boston, MA 02210

(Address of Principal Executive Office)(Zip Code)

Registrant’s Telephone Number, including Area Code: (415) 670-2000

The Corporation Trust Company

1209 Orange Street

Wilmington, DE 19801

(Name and Address of Agent for Service)

With Copies to:

MARGERY K. NEALE, ESQ.	BENJAMIN J. HASKIN, ESQ.	EDWARD BAER, ESQ.
WILLKIE FARR & GALLAGHER LLP	WILLKIE FARR & GALLAGHER LLP	BLACKROCK FUND ADVISORS
787 SEVENTH AVENUE	1875 K STREET, N.W.	400 HOWARD STREET
NEW YORK, NY 10019-6099	WASHINGTON, D.C. 20006-1238	SAN FRANCISCO, CA 94105

It is proposed that this filing will become effective (check appropriate box):

¨     Immediately upon filing pursuant to paragraph (b)	x    On February 13, 2015, pursuant to paragraph (b)
¨        60 days after filing pursuant to paragraph (a)(1)	¨        On (date) pursuant to paragraph (a)(1)
¨        75 days after filing pursuant to paragraph (a)(2)	¨        On (date) pursuant to paragraph (a)(2)

If appropriate, check the following box:

x The post-effective amendment designates a new effective date for a previously filed post-effective amendment.

Explanatory Note

This Post-Effective Amendment No. 138 to the Registrant’s Registration Statement on Form N-1A is being filed pursuant to paragraph (b)(1)(iii) of Rule 485 of the Securities Act of 1933, as amended (the “1933 Act”), solely for the purpose of delaying, until February 13, 2015, the effectiveness of the registration statement for the iShares Core Allocation Conservative ETF, iShares Core Allocation Growth ETF, iShares Core Allocation Moderate ETF and iShares Core Allocation Moderate Growth ETF (the “Funds), filed in Post-Effective Amendment No. 20 on September 9, 2013, pursuant to paragraph (a) of Rule 485 of the 1933 Act.

The effectiveness of the Registration Statement of the Funds was previously delayed pursuant to paragraph (b)(1)(iii) of Rule 485 of the 1933 Act as follows:

PEA No.	Date Filed	Automatic Effective Date
29	November 22, 2013	December 20, 2013
40	December 19, 2013	January 17, 2014
47	January 16, 2014	February 14, 2014
55	February 13, 2014	March 14, 2014
68	March 13, 2014	April 11, 2014
74	April 10, 2014	May 9, 2014
80	May 8, 2014	June 6, 2014
85	June 5, 2014	June 30, 2014
89	June 27, 2014	July 25, 2014
95	July 24, 2014	August 22, 2014
101	August 21, 2014	August 29, 2014
103	August 28, 2014	September 26, 2014
110	September 25, 2014	October 24, 2014
116	October 23, 2014	November 21, 2014
123	November 20, 2014	December 19, 2014
132	December 18, 2014	January 16, 2015

This Post-Effective Amendment No. 138 incorporates by reference the information contained in Parts A, B and C of Post-Effective Amendment No. 20.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all the requirements for the effectiveness of this Registration Statement pursuant to Rule 485(b)(1)(iii) of the Securities Act of 1933, as amended, and has duly caused this Post-Effective Amendment No. 138 to the Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of San Francisco and the State of California on the 15th day of January, 2015.

iSHARES U.S. ETF TRUST 

By:
	Manish Mehta*
	President
	Date: January 15, 2015

Pursuant to the requirements of the Securities Act of 1933, as amended, this Post-Effective Amendment No. 138 to the Registration Statement has been signed below by the following persons in the capacities and on the date indicated.

By:
	Mark Wiedman*
	Trustee
	Date: January 15, 2015
	John E. Martinez*
	Trustee
	Date: January 15, 2015
	Cecilia H. Herbert*
	Trustee
	Date: January 15, 2015
	Charles A. Hurty*
	Trustee
	Date: January 15, 2015

John E. Kerrigan*

Trustee

Date: January 15, 2015

	Robert H. Silver*
	Trustee
	Date: January 15, 2015
	Robert S. Kapito*
	Trustee
	Date: January 15, 2015
	Madhav V. Rajan*
	Trustee
	Date: January 15, 2015
	/s/ Jack Gee
	Jack Gee
	Treasurer
	Date: January 15, 2015
* By:	/s/ Jack Gee
	Jack Gee
	Attorney-in-fact
	Date: January 15, 2015

* Powers of Attorney, each dated December 31, 2013, for Manish Mehta, Mark Wiedman, Charles A. Hurty, Cecilia H. Herbert, John E. Kerrigan, Robert H. Silver, John E. Martinez, Madhav V. Rajan and Robert S. Kapito are incorporated herein by reference to Post-Effective Amendment No. 1,021, filed January 10, 2014.