Beaver Dam Raceway general manager Carolyn Mueller and Bumper to Bumper IRA Outlaw Sprint Car Series President Steve Sinclair confirmed the death.
Beaver Dam police later confirmed that a 47-year-old driver was killed, but did not provide a name.
Semmelmann's car made contact with another car during the second practice session, flipped three times and hit the outside concrete wall. The 47-year-old Semmelmann, from Brookfield, was racing for the first time this season.
"This incident appears to be (a) tragic accident at this time," the police statement said.
The race was canceled.
Beaver Dam Raceway is a 0.33-mile clay oval about 75 minutes northwest of Milwaukee. Mueller said it was the first on-track fatality at the track since the facility re-opened in 1993.
Last month, Kevin Ward Jr. was killed in a sprint car race at a dirt track in upstate New York when he left his car and was struck by a car driven by NASCAR starTony Stewart.
Scott Semmelmann Dies In Crash
ESPN the Magazine's Ryan McGee discusses sprint car driver Scott Semmelmann, who was killed in a wreck during practice at Beaver Dam Raceway.