|Date of birth||18 December 1973|
|Place of birth||Lørenskog, Norway|
|Height||1.88 m (6 ft 2 in)|
|1999||→ Portsmouth (loan)||2||(0)|
|* Senior club appearances and goals counted for the domestic league only.
† Appearances (Goals).
Since 2010, Berntsen is involved with a youth coach role at Lyn.
Berntsen began his playing career at Vålerenga, but failed to make the first team. He spent the next few years in the lower divisions, playing for local clubs Lørenskog IF and Skjetten SK. His breakthrough came in 1998 when he signed for Lillestrøm, where he and his teammate Torgeir Bjarmann made up one of the best central defences in the Norwegian Tippeligaen (Premier Division).
In January 2001, Berntsen left Norway for Germany and Eintracht Frankfurt. His stay, however, was not a success and he only played three matches for the first team. He returned to Norway for a fresh start in December 2001 and was signed by Lyn, where he played since. He acted briefly as a player-coach of the team in 2003. Together with Steven Lustü he once again formed part of a formidable defense. In the 2005 season, no club conceded fewer goals than Lyn. Berntsen has struggled with injuries over several periods, but always remained the captain and featured regularly in the Lyn side the last seasons of his career.