I have been flying in and out of SFO for several months but have not had to switch flights from the domestic terminals to the International Terminal. There used to be a bus located at the lower level near Gate 72 that takes you from SFO Terminal 3 to the International terminal. That bus is no longer available.
SFO has completed a connection bridge that takes you from Terminal 3 to the International Terminal. You will need to walk from the gates of Terminal 3 to the SFO International Terminal via this bridge. The walk way connecting SFO’s Terminal 3 and the International Terminal is near Gate 75 (shown in the map below). It would have been great if travelers received information information about the new bridge at SFO.