Heather Knight's side face the hosts after winning their opening four fixtures, including a 114-run victory over Pakistan on Tuesday.
Despite England's group stage dominance seeing them rise as tournament hopefuls, the weight of hosting the competition is something Wyatt believes builds pressure on their opponents.
"I think the pressure's all on South Africa. It's a home World Cup for them," she said.
"We're just going to keep doing what we're doing. There's such a calm feeling in our group at the minute which is really nice so I think we're not going to change anything.
"Obviously, a semi-final sell-out is going to be really exciting so it's just going to be really important to stay calm, just enjoy each other's company I guess, go out there and back ourselves and what will be will be."
The 31-year-old identified the threats South Africa pose as she singled out players who can hurt her side.
"They got some world-class players in their team," she said. "Obviously they've got (Shabnim) Ismail, (Marizanne Kapp), they have got a great bowling line-up so I'm going to have a think tonight about what their plans might be against us.
"I've faced Kappy and Shabby (Ismail) a lot over my career, my 13 years playing for England, so obviously they know my strengths and weaknesses and I know what theirs are so it's going to be a good battle tomorrow and something I can't wait to be a part of."
England vice-captain Nat Sciver-Brunt has celebrated her £320,000 Women's Premier League deal with 176 World Cup runs at an average of 88 and a strike rate of almost 148, including 81 off 40 balls as she led England to victory over Pakistan in Tuesday's final group-stage fixture.
"She's as cool as a cucumber our Nat, nothing fazes her," said Wyatt. "She's just very chilled, everybody looks at that and you look at her on the field and it feeds around the team.
"Everybody really looks up to Nat and I'm just so glad she's on our team. She's hitting the ball like a beach ball at the minute so hopefully she can keep that up and never change.
"Even when she went for that big pay packet the other day, nothing seems to faze her. She's got a very consistent mood which is key to being a very successful cricketer I think."
Wyatt understands the magnitude of the occasion as she called for calmness in order for her side to progress.
"We've had a lot of success against South Africa so I think we'll take that into the game tomorrow," she said.
"Semi-finals, you know, got to be chilled - just back our plans and got to be brave.
"It's going to be so exciting to play, I've heard it's going to be a sell-out so it's going to be very exciting tomorrow and hopefully it is a sell-out and we can inspire some more young girls to take up the game."