Assam ended their second innings at 338 for four after starting day five at 32 for no loss.
Karnataka were in full control of the quarterfinal ever since bowling out Assam for 185 after scoring 452 in their first innings lead. The Southern team had declared their second innings at 415 for five with Ravikumar Samarth making 178.
Robin Uthappa was named man of the match for his 153 and 77.
Karnataka take on Mumbai in the semifinal to be played in Bangalore from Feb 25-March 1.