The 27-year-old Algerian international, who joined the Hammers from Valencia, has signed for the Turkish Super Lig side a reported 4.5million euros on a five-year deal.
Speaking to his new club, the former Grenoble man said: “I came here to be a champion; I want win the championship. I have to work hard.”
Feghouli played a total of 27 games for West Ham, scoring four goals, including against NK Domzale in the Europa League in the club’s first-ever fixture at London Stadium.
Part of a statement from the Hammers read: “West Ham United would like to thank Sofiane for his efforts and wish him well in his future career.”