The English eves will meet their Australian counterparts in the final on Sunday.
Put into bat, South African women could only manage 101 in 19.5 overs with nine of their batswomen failing to reach double figures.
Mignon du Preez (23) and Chloe Tyron (40) were the only two players who reached double digits, as right arm seamer Anya Shrubsole and left-arm slow medium Rebecca Grundy took two wickets each.
Shrubsole gave away only 12 runs in her four overs and was adjudged the 'Player-of-the-match' for her efforts.
In reply, England scored the runs with as many as 19 deliveries to spare.
Openers Edwards (36) and Sarah Taylor (44 not out) added 67 runs for the opening wicket to wrap up the match in their favour.
Edwards hit five boundaries during her 37-ball knock, while Taylor and the other unbeaten batswoman Heather Knight (21 not out) hit three boundaries each.
Spinner Sune Luus was the only wicket-taker for South Africa.
Brief Scores:
South Africa 101 in 19.5 overs (Chloe Tyron 40, Anya Shrubsole 2/12)
England 102/1 in 16.5 overs (Sarah Taylor 44 no, Charlotte Edwards 36, Heather Knight 21 no).
Image: Heather Knight and Sarah Taylor celebrate winning the Women's World T20 semi-final
Photograph: Scott Barbour/Getty Images
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