Hemský entered pro 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. Hemský 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.
In 2000, Hemský moved to North America to play for the Hull Olympiques of the QMJHL. The following season (2000–2001), Hemský led all rookies in scoring with 36 goals and 100 points. He was named to the All-Rookie team, was selected to play in the 2001 CHL Top Prospects Game, and was awarded the Mike Bossy Trophy as the QMJHL’s top pro prospect.
Hemský continued his success in Hull during the 2001–02 season, with 27 goals and 97 points in 53 games, and finished 19th in the QMJHL scoring race.
2001 NHL Entry Draft
The Edmonton Oilers used the 13th overall pick in 2001 on Hemský. Oilers scout Chris McCarthy said, “We knew that he was the guy that we wanted and when he fell to us, well, we knew who we were going to take.”
The Oilers were able to draft Hemský in part due to a stipulation made in a trade involving star right-winger Bill Guerin to the Boston Bruins. The Oilers were to receive Anson Carter, a 2001 second-round pick, and the option of switching first-round picks in the 2001 or 2002 draft. In 2001 the Oilers chose to exchange their original first-round selection (19th overall) for the Bruins’ (13th overall).
During Hemský’s rookie NHL season, he scored 6 goals and 30 points in 59 games, and was a healthy scratch for 23. He also went pointless in all 6 of Edmonton’s playoff games.
The 2003–04 season saw Hemský take more initiative. Hemský received more minutes on the top two lines. He worked to improve his backchecking, and found his scoring touch on a more regular basis than in his rookie year. When the 06/07 NHL regular season came to an end, Ales Hemský and Petr Sýkora led the Edmonton Oilers in scoring points with 53 points each.
Hemský returned to the Czech Republic to play 47 games for HC Moeller Pardubice during the 2004 NHL Lockout. During that time, he scored 13 goals and 31 points, fifth on the club. Pardubice won the Extraleague championship for the first time in 16 years, and Hemský was named playoff MVP for his efforts.
2005–06 regular season
During the post-lockout 2005–06 season, Hemský had a career year, setting personal bests in every major statistical category. He scored 19 goals, 58 assists and 77 points, while playing in all but one game for the Oilers during the regular season. The Oilers captured the 8th and final playoff seed in the Western Conference. The Oilers went on to eliminate the Red wings in six games in round 1, then beat the San Jose Sharks in games as well in round two. In the Conference finals the Oilers knocked off the Anaheim Ducks in five games. The Oilers lost the Stanley Cup finals in seven games to the Carolina Hurricanes.
2006 Winter Olympics
Hemský was selected to represent the Czech Republic in the 2006 Winter Olympic Ice Hockey tournament mid-season. Czech hockey icon Jaromír Jágr had a large influence on Hemský’s selection, to the point where he insisted that Hemský skate on his line. The two had previously played together on the Czech team that won the 2005 IIHF World Ice Hockey Championships during the NHL’s 04–05 lockout season. Hemský scored twice in the Olympic tournament, and the Czech Republic defeated Russia in the bronze-medal game.
During the 2006 NHL playoffs, Hemský was an important part to the Oilers run to the Stanley Cup Finals. Among his opportune goals were two he scored in the third period of game six versus the Detroit Red Wings, including the series-winner. Hemský underwent a biopsy on an inflamed lymph node on the right side of his neck during the playoffs. Results have not been made public.
Edmonton re-signed Hemský in the summer of 2006 to a six-year contract that will see him earn US $24.60 million.
2006–07 regular season
The 2006–07 campaign saw Aleš Hemský notch 53 points in 64 games. Hemský missed 18 games due to shoulder injuries. In 64 games, Hemský scored 13 goals and added 40 assists with 40 penalty minutes. He also scored a memorable goal on Marty Turco with 2 seconds to go in the 3rd period after Patrik Štefan missed an empty net in a game vs. the Dallas Stars.
2007–08 Joey Moss Cup and off-season
On September 16, 2007, in Grande Prairie, Alberta, Aleš Hemský scored 3 goals and added 2 assists for 5 points to help his team win the Joey Moss Cup by a score of 9-4. Hemský developed good chemistry on a line with teammates Dustin Penner and Sam Gagner. On October 2, 2007, Hemský was named an alternate captain, along with Shawn Horcoff, Steve Staios and Jarret Stoll.
2007–08 season end
The 2007–08 campaign was a short one as the Oilers were eliminated from playoff contention. Hemský finished first on the team overall in points scoring with 71, and was first in assists with 51. He sat in third place for goals with 20, which was a career high for Hemský.
2008 IIHF Inline Hockey World Championships
Hemský was a member of the Czech Republic national team that participated in the 2008 Men’s World Inline Hockey Championships that were played in Bratislava, Slovakia. Hemský tied for fourth place in scoring with 6 goals and 5 assists while leading the Czech Republic to a 5th place finish.
2008–09 season end
The 2008-2009 campaign was another that saw injuries for Hemský, who played 72 out of the 82 regular season games and finished first on the team with 23 goals and 43 assists for 66 points.
2009-2010 regular season
Hemský recorded seven goals and 15 assists during the first 22 games of the 2009-2010 season before suffering a left shoulder injury following a check from behind by Los Angeles Kings forward Michal Handzuš. The injury will require surgery and Hemský is going to miss the remainder of the regular season.
- Edmonton Oilers team record for fastest 2 goals ever scored in a regular season game: span of 7 seconds. (shared with Sheldon Souray)
 Honours and Awards
- Hemsky was to also represent the QMJHL in the 2001 CHL Top Prospects Game,
but an injury forced him to withdraw.
- 2001 QMJHL Rookie of the Month (January)
- 2002 QMJHL 2nd All-Star Team
- 2002 CHL 3rd All-Star Team
- 2005 Czech Extraliga Playoff MVP