Zouma, who was strongly linked with a move to Manchester United in the January transfer window, has extended his stay at the Ligue 1 club to 2017.
In a club statement, Zouma said: "This extension is a great vote of confidence in me from the club. St Etienne means a lot to me because it is where I was developed.
"This is a new step in my career. I still need to learn. I will also gain experience and I know that will help me to grow."
Zouma has made 27 league appearances for St-Etienne.