A representative from the coroner's office identified the jumper as Ram Saripalli, a 41-year-old Fremont man.
A local eyewitness to the event described the scene as "horrific."
Mountain View resident James Harris said he saw what appeared to be a man in his 20s or 30s plunge into oncoming traffic at about 10:45 a.m. as he was driving north on the freeway.
"Just before I was about to go under the (Rengstorff Avenue) underpass, something caught my eye and I looked up to see the last 10 or 20 feet of this body falling," Harris said, noting that the body hit the ground almost parallel to the pavement.
He did not see the beginning of the fall, though the person did leave the overpass on the side closest to oncoming traffic.
Harris' two granddaughters — 2 and 4 years old — were in his car at the time. He said they did not see the body falling, or the aftermath, as they were absorbed in a video they were watching from the backseat. He said he was thankful they did not witness the incident.
The incident was initially reported by the CHP as occurring at the San Antonio Road overpass.
There were major traffic impacts in the area, as several lanes on Hwy. 101 in both directions were shut down for a time.