Career
Berntsen played for Norwegian club Tromsø Illinois and played 146 games for them in the Tippeligaen. Berntsen had played for Tromsø in his youthyears and came back in 1991 after living at Svalbard for one year. He made his debut in the Tippeligaen in 1991.
In 1992, when he was living in Oslo, he joined Vålerenga IF. After he moved back the following year he played three season for Tromsdalen UIL before he again joined Tromsø in 1996.
He also played two European Cup Winners Cup games for them. He joined Portuguese Vale on loan in November 1998 and played in a First Division match on 14 November 1998, in a 2–0 home defeat to Sunderland.
He left the club at the end of the month and returned to Tromsø. He played his last game for Tromsø in October 2001, and retired in the following season due to an injury.