Raonic called a trainer after dropping serve for the second time to trail 5-2 in the first set. Following a short discussion with the doctor, who had a close look at his strapped right foot, the big-serving player from Thornhill, Ont., went to see Berdych on the other side of the court to inform him of his decision to give up.
Berdych, who lost to Rafael Nadal in the semifinals in 2007 and was stopped by Novak Djokov three years ago, will next face 14th-seeded Gael Monfils of France. Monfils followed up his convincing win over Roger Federer in the previous round with a 6-1, 6-3 defeat of ninth-seeded Grigor Dimitrov.
Berdych has yet to lose a set this week at the clay-court Masters tournament.
Nadal, an eight-time champion in Monte Carlo, will later play David Ferrer, and top-ranked Novak Djokovic will face Marin Cilic.
Monfils, who decided to play at the last minute this week after recovering from a right hip injury sooner than expected, was in control as he progressed to the semifinals for the first time.
The Frenchman got off to a strong start and dictated from the baseline to convert his three break points in a 24-minute opening set. Dimitrov was better at the start of the second set but Monfils fended off two break point in the third game with consecutive winning serves, then held after a superb rally punctuated by a cross-court winner just behind the net.
Monfils then broke for a 3-1 lead and sealed his win after Dimitrov could not return a forehand attack.