The woman's 57-year-old male roommate, who has not been identified by the sheriff's office, called dispatchers around 7 a.m. and said that he had shot his roommate at the home in the 18600 block of Bucknall Road, near the border with West San Jose.
When sheriff's deputies arrived shortly after 7 a.m., they told the man to leave the home and arrested him without incident.
The woman, whose name has not been released, was suffering from one or more gunshot wounds. She was taken to a hospital, where she later died.
Homicide and crime scene investigators from the sheriff's office were processing the scene for evidence and conducting interviews as of noontime Thursday.
Anyone with information about the shooting has been asked to call sheriff's investigators at (408) 808-4500. Those wishing to remain anonymous can call (408) 808-4431.