World number one Swiatek improved her record at Roland Garros to 26-2 after beating Gauff for the seventh time in as many meetings.
The 22-year-old from Poland is chasing a third French Open crown and attempting to become the first woman to successfully defend the title in Paris since Justine Henin in 2007.
After the pair exchanged breaks in the fourth and fifth games, Swiatek landed the key blow with another break as Gauff served to stay in the first set.
The American teenager, who won only four games in the 2022 final, made this a much closer contest but was left to rue three missed break point opportunities early in the second set.
Swiatek's quality then shone through as she won the final four games to become the youngest woman since Martina Hingis to reach three or more semi-finals at Roland Garros.
"It wasn't easy, the first set was really tight. Coco was really using the conditions, so I was happy to be able to work on it and win this match," said Swiatek, who has yet to drop a set at the tournament.
