In 2003, the WCHL would end up going out of business. The league and the surviving teams in the league, including the Steelheads, would join the ECHL.[1]
On October 17, 2003, the Idaho Steelheads would play their first game in the ECHL. They would be defeated by the Las Vegas Wranglers 5–3.[2]
The team would be successful in their first season in the league. They finished with 40 wins, 23 losses, and 89 points and would make it all the way to the Kelly Cup finals. They would win their first Kelly Cup after defeating the Florida Everblades four games to one.[3] In the 2006–07 season, the Steelheads would once again make it to the Kelly Cup Finals. They would win their second Cup when they would defeat the Dayton Bombers four games to one.[4]
The Steelheads and the Dallas Stars are affiliates. The Steelheads were formerly the affiliates of the Phoenix Coyotes.[5]