Schalken in 1994 joined the professional tennis at. Since 1996 he is member of the Dutch Davis Cup team.
His athletic most successful year was 2003 when he won the ATP tournaments in Rosmalen and Costa do Sauipe and in the tennis world rankings to No. 11 (21 April 2003) penetrated. Since 2004 he is suffering from the after-effects of a virus infection. Negative highlight in 2004 was the disqualification Schalkens at the Miami Open to Guillermo Cañas in the score of 6:1 and 3:0 for the Argentines. The exact situation is not known, it can be assumed that the strong wind, which usually blows this time of year there, had greatly disturbed the game.
From 2005 Schalken tried in vain to reconnect with his old performances. In February 2006 he took part in a well-staffed Challenger tournament in Bergamo (Italy) and reached the semi-finals. On 29 March 2007 Schalken result of his injuries announced his retirement from professional tennis.