Lufthansa flights from Chennai to San Francisco

Lufthansa and United both fly from Chennai to San Francisco with a stop in Frankfurt. The shortest amount of time the flight will take you is around 24 hours total (although if you choose a longer layover in Frankfurt, the total journey time can
go up to as much as 31 hours.)

I'm afraid there doesn't appear to be a carrier that makes a stop in Amsterdam when flying from Chennai to San Francisco.

Contrary to what the answerer above said, I was unable to find a flight with British Airways that connected in Frankfurt or Amsterdam when flying between the two cities you selected; there are, however, BA flights that go via London Heathrow.

Best option is

Chennai-Amsterdam ( KLM), Amsterdam-San Francisco ( North-West)

Chennai-Frankfurt ( Lufthansa), Frankfurt-SA ( Lufthansa)