In 2001, Semenov was awarded the Max Kaminsky Trophy as the best defenceman in the Ontario Hockey League (OHL). After playing three full seasons for the Oilers and their top farm club, the Hamilton Bulldogs, he was traded to the Florida Panthers for a conditional draft pick in the 2006 NHL Entry Draft on November 19, 2005. Upset at his assignment to the Rochester Americans at the start of the 2006–07 season, Semenov left Rochester after four games to play for Salavat Yulaev Ufa in Russia. On July 27, 2007, Semenov signed a one-year contract with the San Jose Sharks.