Hemphill, a second generation racer, started his racing career at the age of 12, when his father put him behind the wheel of a go-kart.
At the age of 15, Hemphill advanced to Legacy cars (three-quarter scale Nextel Cup cars), where he competed for 2 years and amassed 5 wins and 3 poles including winning the Blue-Grey Shootout at the Jennerstown Speedway(PA) and the Fireball Roberts Memorial at the famed Hickory Motor Speedway (NC).
He expanded his ASA schedule and competed in 6 events with a season best 6th-place finish at the Chicago Motor Speedway.
Hemphill made himself known in 2002 and 2003 driving in the NASCAR Craftsman Truck Series for multiple owners, including Rick Ware, Bobby Hamilton, and Billy Ballew.
In 2005, Hemphill was promoted to the NASCAR Busch Series in the Biagi Brothers Racing Ganassi-assisted program, driving the No.