The collision was reported at 6:19 a.m. at Alum Rock Avenue and South 33rd Street. Police said the woman was hit by a white 2000 Chevrolet pickup.
She was taken to Regional Medical Center of San Jose with injuries that police believed could be life-threatening.
The driver remained at the scene of the collision and is cooperating with investigators, according to police.
Police said alcohol does not appear to have been a factor in the accident.
As of about 7:30 a.m., the eastbound lanes of Alum Rock Avenue and the southbound lanes of South 33rd Street were still closed.