Six-time US Open champion Williams dismantled Chinese 18th seed Wang 6-1, 6-0 in a complete mismatch that was the quickest at this year's tournament to set up a semi-final clash with Ukrainian trailblazer Elina Svitolina.
Williams brought up a century of US Open wins to move to within one of the all-time leader Chris Evert.
"It's really unbelievable, literally. From when I first started here, I think I was 16, I didn't think I would ever get to 100. I didn't think I would still be out here," Williams said.
The 37-year-old American is seeking a 24th major title to match Margaret Court's longstanding record, and smacked 25 winners against first-time Slam quarter-finalist Wang, who failed to hit a single one.
The 27-year-old Wang had not lost a set during her best Slam run that included a defeat of reigning French Open champion Ashleigh Barty in the last 16, but she was powerless to stop a Williams onslaught at Arthur Ashe Stadium.
"When I play someone who is playing really well, I know I have to either step it up or go home and I wasn't ready to go home. I had to come out here and play really well," said Williams, suffering no ill effects from the ankle she rolled in her previous match.
Wang, trying to become just the fourth Chinese player to reach the last four of a Slam, won just four points in the second set and 15 in total.
"It's not easy to play against her," Wang said. "The power, like, I cannot handle it. Just too much for me."
Williams captured her last Slam title at the 2017 Australian Open while pregnant and hasn't won the US Open since 2014.
Svitolina holds
off Konta
Fifth seed Svitolina defeated Britain's Johanna Konta 6-4, 6-4 to become the first Ukrainian to reach the US Open semi-finals, matching her run to the last four at Wimbledon in July. "It feels amazing. It was a very, very tough match. We were both striking the ball well. It was quite even," Svitolina said. "I'm very, very happy the way I handled the pressure." Svitolina watched a pair of match points pass her by at 5-3 on her opponent's serve as Konta gamely fought to stay alive, but the Ukrainian closed out victory in the following game.