A 6-foot-9 center from the University of Minnesota, Hermsen began his professional career with the Sheboygan Red Skins of the National Basketball League in 1943–44 and 1945–46.

He scored 11 points in 12 games during his rookie campaign, but played a greater role in his second season, scoring 55 points in 21 games.

Both Red Skins teams advanced to the NBL championship series — losses to the Fort Wayne Zollner Pistons and Rochester Royals.

Hermsen then played six seasons (1946–1951; 1952–1953) in the Basketball Association of America and National Basketball Association as a member of the Cleveland Rebels, Toronto Huskies, Baltimore Bullets, Washington Capitols, Chicago Stags, Tri-Cities Blackhawks, Boston Celtics, and Indianapolis Olympians.

This biographical article relating to a United States basketball player, coach, or other figure born in the 1920s is a stub.