Officers were dispatched to the 1500 block of El Verano Way on a report of a suspicious vehicle at about 10:25 p.m.
A passerby called the Police Department and reported there was a white Explorer parked on the street. The caller said it had been there for a while and that someone appeared to be sleeping in it.
Responding units found a woman inside who had suffered major trauma. She was not responsive, and an EMT from the Belmont-San Carlos Fire Department pronounced her dead at about 10:35 p.m.
Detectives from the Belmont Police Department and the San Mateo County Crime Lab and the coroner's office responded as well.
Anyone with information regarding the incident is asked to call Detective Dave Lashley or Detective Peter Lotti at (650) 595-7400.