The American, 37, overpowered the Ukrainian fifth seed to win 6-3 6-1.
Williams, seeded eighth, is aiming for her first Grand Slam win since giving birth in September 2017.
The six-time champion will face Canadian 19-year-old Bianca Andreescu in Saturday’s final in New York.
In a gripping encounter, Andreescu defeated 22-year-old Swiss Belinda Bencic 7-6 (7-3) 7-5, winning the last five games of the match.
Williams underlines why she is favourite for victory
Williams is already considered by many as the greatest female player ever, yet will not be satisfied herself until she has levelled – and then overtaken – Australian Margaret Court’s total of all-time Grand Slam singles titles.
Following the difficult birth of daughter Olympia two years ago which almost cost Williams her life, she has reached consecutive Wimbledon finals – plus last year’s controversial US Open showpiece against Naomi Osaka – without capping what has already been a remarkable comeback with another major win.
For Williams to not go on and win a seventh US Open title – an Open era record in the women’s singles – would be a major shock on the evidence of her performances over the past two weeks.
Free of the knee injury which bothered her earlier this year, she is looking as sharp, powerful and clinical as she has in a long time.
That was illustrated by the ease with which she swatted aside Svitolina, the highest ranked player to reach the last eight at Flushing Meadows and competing in her second successive Grand Slam semi-final.
The 24-year-old Ukrainian has one of the most impenetrable returning games on the WTA Tour, yet even she could not keep Williams at bay.
After a slow start where Svitolina could conceivably have led 2-0, it was the American who broke at the first attempt and from that point it was all one-way traffic.
Williams found her range quickly and dominated with her powerful, precise hitting which resulted in 33 winners in a match which lasted only one hour and 10 minutes.
“The first two games were long games and I know how she can play – she is a good player,” Williams said.
“I wanted to not get off to a slow start and I wanted to hang in there.”
Svitolina was expected to provide a tougher test for Williams after clinically dispatching British number one Johanna Konta in their quarter-final on Wednesday.
With her fleet of foot and ability to return, she would have been hoping to withstand everything fired by Williams and then outlast her older opponent.
But even she could not cope with the pummelling produced by the American.
Svitolina’s inability to take any of six break points in the early part of the first set proved terminal to her hopes.
Helped by three unforced errors from Williams in the opening game, Svitolina created three break points which she could not convert and then saw her illustrious opponent fight back from a 0-40 deficit to break for a 2-0 lead after a hard-fought 15 minutes.
Another 0-40 lead disappeared as Williams held for a 4-1 lead and from that point Svitolina’s confidence sapped, along with her ability to push her opponent.
“I just wish I could have taken those opportunities,” said Svitolina, who won the season-ending WTA Tour Finals last year.
“It could be maybe a 2-2 or 3-3 instead of 0-3, which allows you to push to play more freely.”
In the second set she was not able to touch Williams’s serve, winning just three receiving points.
“She has unbelievable strength. She gives lots of power,” Svitolina said.
“There’s lots of power behind her shots all the time. That’s what makes her an unbelievable, legendary tennis player.”