He also served as an assistant coach of the San Jose Sharks. Since 1998, he has been the head coach of the San Jose Barracuda, the American Hockey League affiliate of the Sharks. Currently, he is the longest-tenured head coach in the AHL.
On November 1, 2009, Sommer became just the fourth head coach in AHL history to reach 400 wins.
On February 10, 2016, Sommer became just the winningest head coach in AHL history when he reached 637 wins.
He surpassed Bun Cook who spent 19 seasons as a head coach in the AHL.