The Grand Slam champions are bidding to reach their first World Cup final, with Gatland making three changes from the team that edged past France in the quarter-final.
Leigh Halfpenny and Ross Moriarty come in to replace the injured Liam Williams and Josh Navidi, both of whom have been ruled out for the remainder of the tournament.
The final change sees Jonathan Davies return from the knee injury that forced him to withdraw from the clash with France.
And for Gatland, who will step down as Wales coach at the end of the tournament, he is happy to keep flying under the radar, even if he admits to being a little confused as to why.
He said: “The nice thing about being out here is that you are kind of in a bubble and you are not seeing a lot of the stuff externally.
“If they continue to (write us off) over the next couple of days that would be brilliant. Please continue to do that as it does get us up when people write us off.
“I can’t understand why people would write us off when our record against South Africa has been pretty good in the last four or five years. That speaks for itself.”
Alun Wyn Jones will captain the side as he wins his 142nd Test cap, moving level with Sergio Parisse for second place all time.
Meanwhile Dan Biggar, who will keep the kicking duties, will start alongside Gareth Davies, who wins his 50th cap.
On the bench there are two changes, with Owen Watkin dropping down from the starting XV, while Aaron Shingler steps in with Moriarty promoted to the starting line-up.
FIRST LOOK 🔴 Wales’ team for the #RWC2019 semi-final against South Africa at #RWCYokohama Mi fydd @Gar_Davies9 yn ennill ei 50fed cap yn erbyn y Boks. #HWFN pic.twitter.com/HxPiWTbOZs
— Welsh Rugby Union 🏉 (@WelshRugbyUnion) October 25, 2019
Wales team to face South Africa:
15. Leigh Halfpenny (Saracens)
14. George North (Ospreys)
13. Jonathan Davies (Scarlets)
12. Hadleigh Parkes (Scarlets)
11. Josh Adams (Cardiff Blues)
10. Dan Biggar (Northampton Saints)
9. Gareth Davies (Scarlets)
1. Wyn Jones (Scarlets)
2. Ken Owens (Scarlets)
3. Tomas Francis (Exeter Chiefs)
4. Jake Ball (Scarlets)
5. Alun Wyn Jones (Ospreys) (c)
6. Aaron Wainwright (Dragons)
7. Justin Tipuric (Ospreys)
8. Ross Moriarty (Dragons)
Replacements:
16. Elliot Dee (Dragons)
17. Rhys Carre (Saracens)
18. Dillon Lewis (Cardiff Blues)
19. Adam Beard (Ospreys)
20. Aaron Shingler (Scarlets)
21. Tomos Williams (Cardiff Blues)
22. Rhys Patchell (Scarlets)
23. Owen Watkin (Ospreys)
