Witnesses spotted the victim's body in the center divider of Highway 99, just south of Yosemite Parkway in Merced.
Officers say someone ran over the 42-year-old man and then left the scene. Investigators believe the crash happened between 3 a.m. and 10:30 a.m. Friday, but they do not have a vehicle description.
Anyone with information is asked to call CHP.