Thiem defeated 21st seed de Minaur 6-1, 6-2, 6-4 to become the first Austrian ever to reach the last four at the Flushing Meadows.
Second-seed Dominic Thiem defeated Alex de Minaur in straight sets to reach the semi-finals of the US Open for the first time.
In a quarter-final clash that lasted for two-hour and four minutes on Wednesday, Thiem defeated 21st seed de Minaur 6-1, 6-2, 6-4 to become the first Austrian ever to reach the last four at the Flushing Meadows.
"I had a great feeling from the first moment on," said Thiem, who will now face 2019 US Open finalist Daniil Medvedev for a place in the summit clash.
"There is no Roger, Rafa, Novak, but there is Daniil, Sascha and Pablo now," he said. "There are three other amazing players. Every single one of us deserves this first major title. Everybody will give it all. Once we step on the court, those other three are forgotten anyway," he added.
Thiem had last reached the quarterfinals in New York in 2018. After battling Rafael Nadal for four hours and 49 minutes in an all-time slugfest before falling short in a fifth-set tie-break, the Austrian said the match was, "going to be stuck in my mind forever".
In the second semifinal, Alexander Zverev will take on Pablo Carreno Busta on Saturday.
