Authorities reported the crash around 6:30 p.m. It appeared the semitruck was mostly blocking the Lake Avenue offramp.
At one point, it was reported that good Samaritans tried to get the driver out the semitruck after the vehicle turned over. Authorities reported overnight Wednesday that the driver died.
He was identified as Jamie Paz, 60, of Fontana.
It was unclear what caused the crash.
A SigAlert was issued for the offramp and westbound traffic appeared to be backed up for a few miles as vehicles moved slowly through the area.
Authorities said there may be a two to three hour detour until the scene is cleared.