The 19-year-old dropped just two games as she blitzed Jelena Ostapenko 6-0 6-2 inside Arthur Ashe Stadium.
Latvian Ostapenko, the 20th seed, had blown the women’s draw wide open when she knocked out defending champion and world number one Iga Swiatek in round four.
But she was unable to take advantage of her own handiwork as Gauff raced away with the first set in only 20 minutes.
Ostapenko made more of a contest of it in the second set, finally managing to hold serve at the fifth attempt.
But Gauff completed the job in an hour and eight minutes to reach the last four of her home grand slam for the first time.
“It feels great, I’m so happy,” she said. “Last year I lost in the quarter-finals and I wanted to do better. There’s a long way to go but I’m happy and ready to go back to work.
“Honestly, I didn’t feel comfortable the whole match, even on match point. I know the game she plays. It’s really tough against her – you can’t really be aggressive. She’s a top player and she’s had a great tournament.
“There’s a saying in basketball that ‘defence wins games’. It doesn’t always work in tennis but today that was the case.”
Gauff will face the winner of Tuesday night’s match between Sorana Cirstea and Karolina Muchova in the last four.
