Hemsky entered in hockey as a 16-year-old, playing for HC Moeller Pardubice of the Czech Extraliga, in his hometown of Pardubice. He split the 1999–2000 season between Moeller and their junior club, HC Moeller Pardubice Jr. Hemsky decided he had a better chance to be scouted if he played Canadian Junior hockey than if he tried to make the jump to the Czech Extraleague, and he subsequently became the first selection of the Hull Olympiques in the 2000 CHL Import Draft.An offensively gifted player, Hemsky spent two seasons with the Olympiques registering 63 goals and 197 points before making his NHL debut with the Oilers in 2002-03. In his first full season in the NHL, Hemsky tallied six goals and 24 assists for 30 points, before improving on those totals in 2003-04. During the NHL lockout in 2004-2005 Hemsky played 47 games for his hometown HC Moeller Pardubice of the Czech Republic Extraleague and registered 31 points. While competing with Pardubice Hemsky was named playoff MVP as the club won the league championship.
In the 2005-06 season, Hemsky returned to the Oilers and blossomed offensively scoring a career high and team leading 77 points. His offensive contribution toward the end of the regular season helped the Edmonton Oilers sneak into the 2006 NHL playoffs. Hemsky and the Oilers took the league by surprise defeating each divisional champion en route to the Stanley Cup Finals. However, in the final round of the playoffs the Oilers would finish one win short of their goal. Hemsky tallied five game winning goals during the 2006 playoffs in what would be his breakout season with the Oilers. He was selected to represent the Czech Republic in the 2006 Winter Olympic Ice Hockey tournament mid-season.