Swiss star Federer was too good for his Dutch opponent Photos from the match Gamewatch: All the action

The Swiss player, the highest seed left in the draw, ran out a 6-3 6-4 6-4 winner and will now face Andy Roddick in the last four.

Federer had been complaining of a sore back going into the quarter-finals but showed no sign of discomfort as he produced an almost flawless display of silky-smooth tennis.

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Schalken, who was also troubled by injury ahead of the match after aggravating a foot problem, did not play badly but could not cope with Federer's barrage of winners.

The fourth seed admitted it had not been easy competing against an unfit opponent, despite his own injury worries.

I've been waiting a long time for this moment Roger Federer More quarter-final reaction

"Today I definitely wasn't at my best," he said.

"When you know your opponent is injured, you pay a bit more attention to it but in the end it doesn't matter - I am very happy to be in the semis for the first time.

"I'm sorry he couldn't do better but I have been waiting a long time for this moment."

One break in both of the first two sets was enough to put the 21-year-old well on the way to victory.

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A brief lapse of concentration allowed Schalken to take a 3-0 lead in the third set but Federer, whose mental game has often let him down in the past, was able to regroup.

The world number five rattled off six of the next seven games to clinch victory in one hour and 37 minutes.