American Williams, 37, is aiming to match Australian Margaret Court's record of Grand Slam singles titles.

Fifth seed Svitolina is the highest ranked player left in the women's event and beat Britain's Johanna Konta 6-4 6-4 in the quarter-finals on Tuesday.

"Elina is obviously a fighter, she gets a lot of balls back," said Williams.

"She doesn't make a lot of mistakes. She's one of those players that does everything really well so I have to do everything well, too."

Seeded eighth, Williams is looking for her seventh US Open title but her first since 2014.

She has won four of her previous five matches against the 24-year-old Ukrainian but Svitolina's victory came in their most recent meeting - a last 16 match at the 2016 Olympic Games in Rio.

"It was an unbelievable atmosphere. I played actually a great match," said Svitolina. "I was kind of young and didn't have big wins at that time.

"It gave me the confidence to actually let me believe I can play consistent against the top players."

Serena Williams' match with Elina Svitolina starts at 00:00 BST on Friday, 6 September

Williams' victories at Flushing Meadows in 2019 have included wins against former world number one Maria Sharapova, 22nd seed Petra Martic and the American needed only 44 minutes to thrash China's 16th seed Qiang Wang 6-1 6-0 in the quarter-finals.

However, Svitolina, who also reached the final four at Wimbledon earlier this year but has never played in a Grand Slam final, has also been in impressive form and has not dropped a set in five matches.

She beat Serena's sister Venus, herself a two-time US Open champion, in round two, American 10th seed Madison Keys and then Konta in the last eight.

"I have to react quickly and try to take my chances when I have them," Svitolina added.

"I have played some big hitters in this tournament and I have to react quickly with my feet and with my shots. Then when I have the opportunity, go for it."

'I was dreaming about this day coming'

Belinda Bencic had not reached the quarter-final of a Grand Slam before this tournament

In the other semi-final, 13th seed Belinda Bencic of Switzerland takes on 19-year-old Canadian Bianca Andreescu.

Bencic knocked out 2018 champion and world number one Naomi Osaka 7-5 6-4 on Tuesday and backed that up with a win over Croatia's Donna Vekic, the 23rd seed, on Wednesday.

That victory took Bencic into a Grand Slam semi-final for the first time in her career.

"Semi-final feels great right now," she said. "I was dreaming about this day coming but you never know. I worked hard for this."

Bencic sank as low as 328th in the world rankings after numerous injuries and surgery on her left wrist two years ago but is guaranteed to return to the top 10 for the first time since June 2016.

Andreescu, meanwhile, will also enter the top 10 after coming from behind to beat Belgium's Elise Mertens in the quarter-finals.

The Canadian, who has won two WTA titles this year, is also making her first appearance in the last four at a Grand Slam.

Murray aims for another doubles final

In the men's doubles semi-finals, British pair Jamie Murray and Neal Skupski take on top-seeded Colombians Juan Sebastian Cabal and Robert Farah, who won the doubles title at Wimbledon in July.

Murray and Skupski won a thrilling final-set tie-break against Americans Jack Sock and Jackson Withrow, while Cabral and Farah eliminated the pairing of Britain's Luke Bambridge and Japan's Ben McLachlan.

Murray is on course for two doubles titles as he is also in Saturday's mixed doubles final, partnering American Bethanie Mattek-Sands. Last year's champions will play either the top-seeded duo of Chan Hao-ching and Michael Venus or fourth seeds Latisha Chan and Ivan Dodig.

This is only the second Grand Slam that Jamie Murray and Neal Skupski have played in together