The 22-year-old, ranked world No. 1 by the Women's Tennis Association (WTA), defeated Brazilian player Beatriz Haddad Maia 4-6, 6-0, 6-2 in their quarterfinal clash on Tuesday.
The Polish player will now face Madison Keys of the United States or Ons Jabeur of Turkey for a place in the championship match at the clay-court tournament in the Spanish capital.
Świątek in March won the BNP Paribas Open tournament at Indian Wells, California, claiming her 19th career singles title.
The Polish star in November regained her spot at the top of the world rankings in women's tennis after winning the season-ending WTA Finals tournament in Mexico.
The Pole, coached by countryman Tomasz Wiktorowski, leads the WTA rankings with 10,560 points, ahead of Belarusian Aryna Sabalenka, with 7,848 points, and American Coco Gauff, with 7,258.
Meanwhile, Poland's Hubert Hurkacz bowed out of the men's singles in Madrid after losing to American Taylor Fritz 6-7, 4-6 in the round of 16 on Tuesday.
(gs)
Source: IAR, PAP, Canal+