Nkosi replaces the hot-stepping Cheslin Kolbe who has not recovered sufficiently from the ankle injury he suffered against Canada and aggravated in the quarter-final victory over Japan (26-3) in Tokyo on Sunday.
The 23-year-old Nkosi – who has scored eight tries in his 10 Test appearances – slots into the right wing position as a direct replacement for Kolbe.
“It’s disappointing not to have Cheslin available as he has been brilliant for us since we first called him up last year,” said Rassie Erasmus, South Africa’s director of rugby.
“But we really rate Sbu and he will slot straight in. I am as excited to see what he can do as I would be if ‘Chessie’ were playing. Sbu has been very close to selection as it is.”
Nkosi has made two appearances in the tournament, against Namibia and a try-scoring show against Canada – on the left wing – to follow up try-scoring appearances against Australia and Argentina (two tries) in the two South African home Tests in 2019.
His injury-enforced inclusion is the only change to the 23 that had been entrusted to ensure second place in the pool (against Italy) and to secure a semi-final place (against Japan).
The Springbok 23 includes 10 players who appeared in the Rugby World Cup quarter-final victory over Wales four years ago in England (23-19), and nine who are making a second semi-final appearance after losing to eventual champions, New Zealand, four years ago.
The nine are Tendai Mtawarira, Frans Malherbe, Eben Etzebeth, Lood de Jager, Francois Louw, Duane Vermeulen, Handré Pollard, Damian de Allende and Willie le Roux. Pieter-Steph du Toit was on the bench in the quarter-final at Twickenham in 2015.
The winner will play the victor of the England v New Zealand semi-final in Yokohama on Saturday, 2 November.
South Africa’s semi-final with Wales kicks off at 11h00 (SA time) and is available on SuperSport channel 201 and SABC radio.
The Springbok team to play Wales in Yokohama on Sunday is:
15. Willie le Roux (Toyota Verblitz, Japan), 59 caps - 60 points (12 tries)
14. Sbu Nkosi (Cell C Sharks), 10 - 40 (8t)
13. Lukhanyo Am (Cell C Sharks), 13 - 15 (3t)
12. Damian de Allende (DHL Stormers), 45 - 25 (5t)
11. Makazole Mapimpi (Cell C Sharks), 12 - 65 (13t)
10. Handré Pollard (Vodacom Bulls), 46 - 421 (6t, 71c, 79p, 4d)
9. Faf de Klerk (Sale Sharks, England), 28 - 20 (4t)
8. Duane Vermeulen (Vodacom Bulls), 52 - 15 (3t)
7. Pieter-Steph du Toit (DHL Stormers), 53 - 25 (5t)
6. Siya Kolisi (captain, DHL Stormers), 48 - 30 (6t)
5. Lood de Jager (Vodacom Bulls) 43 - 25 (5t)
4. Eben Etzebeth (DHL Stormers), 83 - 15 (3t)
3. Frans Malherbe (DHL Stormers), 36 - 5 (1t)
2. Bongi Mbonambi (DHL Stormers), 34 - 35 (7t)
1. Tendai Mtawarira (Cell C Sharks), 115 - 10 (2t)
16. Malcolm Marx (Emirates Lions), 31 - 25 (5t)
17. Steven Kitshoff (DHL Stormers), 45 - 5 (1t)
18. Vincent Koch (Saracens, England) 19 - 0
19. RG Snyman (Vodacom Bulls), 21 - 5 (1t)
20. Franco Mostert (Gloucester, England), 37 - 5 (1t)
21. Francois Louw (Bath, England), 74 - 50 (10t)
22. Herschel Jantjies (DHL Stormers), 9 - 20 (4t)
23. Frans Steyn (Montpellier, France), 65 - 141 (11t, 7c, 21p, 3d)