Sjeng Schalken (born 8 September 1976 in Weert) is a former professional tennis player from the Netherlands.

A right-handed baseliner with a single-handed backhand, Schalken's game is characterised by his consistency of both wings and his continental technique on both the forehand and backhand. The latter is his major weapon, a rallying shot that is also capable of being struck for winners either cross-court or down the line. The player he admired most while growing up was Ivan Lendl.

Schalken is known for his placid on-court demeanour, seemingly reacting in the same manner whether trailing or leading. But as a junior and a young pro he had an explosive temper that, he has stated, hindered him in many matches and caused him to lose through not thinking clearly. Only in 1999 did he manage to suppress his emotional side while on court and develop a more level-headed temperament, although he was disqualified from the Nasdaq-100 Open in 2004 for verbally abusing the umpire.

Schalken turned tennis professional in 1994 having been an outstanding junior, winning the US Open junior event in 1994. He won his first career title on clay in Valencia at the age of 19, defeating Gilbert Schaller in the final. He was the youngest winner on tour for that year, 1995, and the next year as well when he defeated Younes El Aynaoui in the final in Jakarta for his second title. Schalken managed to win at least one ATP tournament eight out of nine years from 1995 to 2003, the sole exception being 1998.