The victim, a 74-year-old woman, was walking on a sidewalk in a neighborhood near Homestead Road and Mary Avenue when a motor home hit her from behind around 7:10 a.m., Capt. Dave Verbruggge said.
The driver of the vehicle fled, he said.
Firefighters and paramedics responded and transported the victim to Santa Clara Valley Medical Center, where she was pronounced dead.
Verbrugge said the woman was visiting family in the area but said police have not yet determined where she lives.
Officers found the motor home a few blocks away at a shopping center and located the driver as he was exiting a business. They took him into custody on a hit-and-run charge.
The man in custody is a resident of Sunnyvale but police are not yet releasing his name. Officers are investigating the circumstances of the collision and have not yet determined whether he was under the influence of alcohol or drugs.
Anyone with information about the collision is asked to call police at (408) 730-7110.