The American will have Andrey Rublev as an opponent on Saturday
Defending champion Stefanos Tsitsipas is out of the Monte Carlo Masters, losing to Taylor Fritz in the quarter-finals on Friday. The Greek player lost the opening four games on his way to a 6-2 6-4 defeat by the American eighth seed.
Fritz, 25, will face Russian Andrey Rublev in the semi-finals on Saturday.
Second seed Tsitsipas had beaten Fritz in three previous hard-court meetings, and had also recorded 12 victories in total on the Monaco clay, dropping only one set.
He levelled the match at 4-4 in the second set but lost out on his serve again to go behind 5-4, before Fritz sealed the win with an ace on his first match point.