The collision, which happened at about 6 a.m. just north of the Silver Avenue exit, involved the motorcycle and a 36-passenger bus, CHP Officer Mark Ferguson said.
The motorcyclist was badly hurt and was taken to San Francisco General Hospital, he said.
There were no passengers on the bus, and the driver was not injured, Ferguson said.
Several lanes were blocked as emergency crews responded, but the roadway was cleared shortly before 8 a.m.
The cause of the accident remains under investigation.