The 31-year-old Dutch international, who joined Schalke from Real Madrid in 2010, is the club's second best scorer since the Bundesliga started in 1963 with 101 goals in 161 matches in all competitions, including 66 in 114 league games.
"The agreement includes an option for a further year of collaboration," Schalke said in a statement.
The Ruhr valley club have reached the Champions League last 16 where they will face Real Madrid.
(Reporting by Karolos Grohmann, editing by Ed Osmond)
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