It finished 6-4, 6-2, 6-1 to the seventh seed after one hour and 50 minutes. The Austrian will play either the 20th seed Novak Djokovic or the unseeded Italian Marco Cecchinato for a place in Sunday’s final.
Zverev, 21, struggled with a leg injury from the end of the first set. With his movement hampered and Thiem displaying the full array of clay court techniques, the German appeared doomed - seemingly paying the price for three successive five set matches before the quarter-final.
"He is one of the fittest guys on the tour but it was difficult for him today," said Thiem. "I hope we have many more matches at the Grand Slams but when we are 100 percent.”
Thiem, 24, is the only man to have beaten Rafael Nadal on clay this season. The victory came in the last eight at the Madrid Masters.
"It's great to reach the semi-finals at the French Open for a third year but it's time to take another step and I will do everything for that."