The USA veteran, 32, departs the Veltins-Arena for the remainder of the 2013-14 campaign but could end up extending his stay at the Turkish club for a further two years
Besiktas have completed the loan signing of Schalke midfielder Jermaine Jones until the end of the season.
The 32-year-old United States midfielder will join Slaven Bilic's side until May, with an option to extend his contract by two years if both the player and the Super Lig club parties are in agreement.
The move essentially ends of Jones' stay at Schalke, with his contract set to expire at the end of the season.
"We are pleased that Jermaine has found a new club, in which he can realise his great sporting goals this year," a statement on Schalke's official website said.
"He can lay the foundation for a successful participation at the World Cup in Brazil.
"Our thanks to him for his efforts in the Schalke jersey in the past seven years. We wish him well in his professional and personal future."
Jones joined Schalke from Eintracht Frankfurt back in 2007 and has made well over 100 appearances for the club, including 14 in the Bundesliga this season and five in the Champions League.
He spent a loan spell with Blackburn Rovers in 2011 and also played for Bayer Leverkusen earlier in his career.