The 18-year-old world No.150 stunned No.17 seed Maria Sakkari 6-1 6-4 to book her spot in the US Open final, where she will meet fellow teenage giantkiller Leylah Fernandez.
Raducanu is only appearing in her second grand slam, having made a run to the fourth round at Wimbledon in June.
The Briton has become the first qualifier in the Open era, male or female, to reach the final of a Major, while she is the youngest grand slam finalist since Maria Sharapova at Wimbledon in 2004.
On top of that, Raducanu is the first British woman to reach a grand slam final since Virginia Wade in 1977.
"The time here in New York has gone so fast," Raducanu said.
"I've just been taking care of each day and before you know it, three weeks later, I'm in the final and I can't actually believe it."
She added during her post-match news conference: "[It is] a surprise. Honestly, I just can't believe it. A shock. Crazy. All of the above.
"It means a lot to be here in this situation. I wanted, obviously, to be playing grand slams, but I didn't know how soon that would be. To be in a grand slam final at this stage of my career … I have no words."
The Canada-born teenager will become only the fourth British woman in the Open era to appear in a grand slam final after Wade, Sue Barker and Ann Haydon-Jones.
Raducanu, who was full of praise for the Arthur Ashe Stadium crowd, added that she was feeling no pressure or expectation.
"Is there any expectation? I'm a qualifier, so technically there's no pressure on me," she said.
Raducanu was glowing in her praise for former British men's No.1 and four-time Wimbledon semi-finalist Tim Henman, who has been in her box during this tournament.
"Tim is honestly such a big inspiration. He's been helping me, telling me to treat it one point at a time," Raducanu added.
"In moments like this, you can't get ahead of yourself and you really have to stay present."
The US Open decider will be the first grand slam final between teenagers since the 1999 edition at Flushing Meadows when Serena Williams (17) defeated Martina Hingis (18).