The Germany international, who has seven goals in 13 games this term, has agreed a move to the Gelsenkirchen side after the club activated his €2.45 million (£2m) release clause
The 25-year-old has long been linked with a transfer to Schalke and the Gelsenkirchen side have now triggered his €2.45 million (£2m) exit clause to secure the Germany international's services.
"Sidney Sam has proven with his superb performances this season that he can offer a lot in attack. He is very versatile and wants to achieve a lot with Schalke. We are very pleased that he has opted to join us," general director Horst Heldt declared.
The pacey forward started his professional career with Hamburg and also wore the Kaiserslautern jersey before joining Leverkusen in the summer of 2010.
Sam has been in sublime form for Leverkusen this term, scoring seven goals and creating five more in 13 appearances.