The 2014 World Cup winner with Germany has been at Schalke since 2001 and cannot envisage leaving a "unique club".
"I have said it before that I will play for no other club in the Bundesliga. At a time of the I, I want to stand for the We. For trust and loyalty," the central defender, currently injured, said in a statement.
"I will defend those words on and off the pitch."
The 27-year-old rugged defender joined the club as a youth player, breaking through to the senior team in 2007.
Schalke are fourth in the Bundesliga, two points off third-placed Hertha Berlin and battling for a Champions League place.
(Reporting by Karolos Grohmann; editing by Justin Palmer)
