Despite having lost her previous six major quarterfinal matches, American Pegula defeated top-seeded Polish player Swiatek 6-2 6-4 in New York.
After Karolina Muchova defeated Beatriz Haddad Maia 6-1 6-4 on Thursday, she will play the Czech in the championship match.
“I’ve been [to the quarter-finals] so many freaking times but I kept losing,” Pegula remarked.
“I can now declare that I’m a semi-finalist at last. I am grateful to the audience for supporting me during the last game.
It’s insane to take on the world’s best player at prime time, but I believed I could pull it off.
Pegula’s victory completes an impressive performance by Americans at their home Grand Slam; in the other semi-final, Emma Navarro, a fellow citizen, will take on Aryna Sabalenka.
Given that Frances Tiafoe and Taylor Fritz will face each other in the final four on Friday, there will undoubtedly be an American guy in the singles championship match.