The girl was struck in what appeared to be an intentional act around 10:45 p.m. at the East Meadow Drive crossing, Caltrain spokeswoman Christine Dunn said.
The girl is the 10th person to be fatally struck by a Caltrain this year, four of which have been deemed suicides, Dunn said.
The Santa Clara County medical examiner's office will determine whether the girl's death was a suicide, though Dunn said the act was likely intentional.
On May 5, a 17-year-old boy was struck and killed by a Caltrain at the same crossing. Messages from officials at Gunn High School, where the boy was a student, indicated his death was a suicide.
Another Gunn student, a 17-year-old girl, was killed by a train June 2 also at the same crossing. Dunn said her death also appeared to be intentional