The crash happened shortly before 6 p.m., according to the California Highway Patrol, near the intersection of Avenue D and 110th Street in Lancaster.
Officials are investigating the cause, but a witness told officers that the semi was heading east on Avenue D while the Jeep heading north on 110th blew through the stop sign at the intersection. The semi tried to avoid the Jeep, but couldn't, and ended up broadsiding the car, overturning.
Six people were injured — the driver of the semi truck and five people in the Jeep. One of the people in the Jeep was declared dead at the scene, while two people in critical condition were airlifted. The other three victims were taken to the hospital by ambulance.
No other information on the crash or the identities of the victims was immediately available.