The 31-year-old, who signed from Barcelona in the summer of 2015, has so far played 131 games for the Blues, scoring 28 times.
The deal means he will remain at Stamford Bridge until 2020.
He told the club’s official website: “It is very good for me, I am really happy here in the club, with my team-mates, the supporters and the club in general.
“It’s important for me to continue with Chelsea, I am comfortable here and want to win new titles and trophies. I want to help the team, score goals, and I repeat, I am really happy.”