Arizona State Route 303, also known as Loop 303 (spoken as three-oh-three) or Bob Stump Memorial Parkway formerly called Estrella Freeway, is a state highway that was maintained by Maricopa County in central Arizona serving the far western suburbs of the Phoenix metropolitan area until 2004 when the Arizona Department of Transportation again took the control of upgrading the interim road to a freeway. As of 2004 it was renamed "Bob Stump Memorial Parkway" to honor former Arizona congressman Bob Stump.

Its current route is from just north of the Cotton Lane exit of Interstate 10 in Goodyear to Interstate 17 south of Carefree Highway. Unlike Loop 101 and Loop 202, most of Loop 303 is currently not a controlled-access highway ("freeway") from Interstate 10, although there are portions currently under construction between I-10 and US 60 to make it a freeway by the end of 2014. The section of highway between Happy Valley Parkway/Vistancia Boulevard to Interstate 17 is currently a controlled-access freeway. Although it has not been fully constructed, portions of Loop 303 from Lake Pleasant Parkway to Interstate 17 officially opened to traffic on May 13, 2011.

Loop 303 begins at an interchange with I-10 in Goodyear. It heads north and intersects McDowell Road and Indian School Road. The road heads through a farmland terrain and passes the Wildlife World Zoo near Northern Avenue. It intersects the BNSF Railway near Olive Avenue. Past an intersection with Greenway Road, Route 303 enters a residential community and turns northeast. The route meets another BNSF railroad line near an intersection with US 60, Grand Avenue. The route turns eastward and becomes a controlled-access highway at El Mirage Road. It turns north near the Happy Valley Parkway interchange and then east again south of Lake Pleasant, coming to an end at an interchange with I-17 near Skunk Creek.

Loop 303 was originally a part of the 1985 Maricopa County Regional Transportation Plan to be funded by a sales tax approved by Maricopa County voters. The freeway, designed to service the Northwest Valley, would have been completed sometime by 2014. However, funding shortfalls and increasing construction costs forced cutbacks in the plan, and in 1995 the freeway was dropped from the regional plans.

Maricopa County took charge of what was then called the Estrella Freeway project when it was dropped from the regional freeway plans, maintaining it as an interim 2-lane highway along the original corridor while keeping the state route designation. The county has made significant improvements to the roadway, extending it several miles north and east of US 60. While the highway is still largely a 2-lane rural road, the extension north of US 60 along with the southern terminus just north of Interstate 10 have been upgraded to a 4-lane divided parkway, and the segment between US 60 and Bell Road in Surprise has been partially upgraded to controlled-highway standards with overpasses and right-of-way for on-ramps.

With the extension of the sales tax approved in 2004, the highway has once again been added to the Regional Transportation Plan. As Maricopa County has completed much of the required study and preparation work, construction on the freeway is already underway with a planned completion date of the I-10 to I-17 segment by 2015. In mid 2011 the segment between Happy Valley Parkway and I-17 was completed as a four lane highway with an interchange at Lone Mountain Parkway completed but closed to the public. Currently, motorists must pass through a signaled interchange until a freeway to freeway interchange is built between Loop 303 and I-17. According to a recent agreement between the state legislature and the state department of transportation, STAN (Statewide Transportation Acceleration Needs) funds were used to build a partial interchange at Bell Road in summer 2010, several years before previously intended.

Long-term plans call for the extension of Loop 303 south of the interchange with I-10 in Avondale to the planned I-10 'Reliever Route' Freeway, SR 30, and continuing south through Goodyear to connect with the planned alignment of future Interstate 11. Loop 303 would run concurrent with I-11 for several miles, before splitting off southward towards its ultimate terminus at Interstate 8 west of Casa Grande. If completed, Loop 303 will serve as a Phoenix bypass route for the southwestern suburbs of Goodyear, Avondale, and Buckeye as well as an alternate Phoenix bypass route for I-10 traffic headed westbound to the Greater Los Angeles Area and northbound via I-17 to Flagstaff.

In response to a projected budget shortfall of $6.6 billion brought on by the recession, the Maricopa Association of Governments voted to suspend funding to numerous projects during a meeting on October 28, 2009. Some modifications to Route 303, such as a scaled-back design of its interchanges with I-10 and US Highway 60, were made to cope with the budget shortfall. Funding for the extension south of I-10 to the planned alignment of SR 30 was removed, effectively postponing the extension until after 2025.

The entire route is in Maricopa County.

^a The City of Glendale has strip annexed land surrounding these exits, though they currently are not within the city's corporate boundaries.