Tech made the announcement Monday afternoon.
This is Thomsen's first year on the Red Raiders' staff. He will fill in after Tommy Tuberville's resignation Saturday to take the head-coaching position at Cincinnati.
Thomsen had a record of 53-18 as head coach at ACU from 2005 through 2011. In 2006, he led the Wildcats to an 8-3 mark and their first appearance in the NCAA Division II playoffs. That was the first of five consecutive postseason trips as his teams went 10-3 in 2007, 11-1 in 2008, 9-4 in 2009 and 11-1 in 2010.