The Bafana Bafana midfielder has had an excellent campaign on loan for The Toffees, who currently lie in fifth place in the English Premiership, though he has yet to find his best form since returning injured from the 2008 Africa Cup of Nations in February.
The 25-year-old joins from Borussia Dortmund for £2.05-million (R32-million) after failing to impress in the last campaign at the Westfalenstadion.
The former Ajax Amsterdam player has made 35 appearances for Everton this season, scoring twice.
"Steven has done well for us,” coach David Moyes told the club’s official site. “He is one of the reasons our football has improved. He is a really good football player."