The 20-year-old Netherlands Under-21 defender joined the Blues from PSV Eindhoven in July 2009.
He has made fleeting first-team appearances for Chelsea, with just three starts in eight outings to his name since his arrival.
But he has gained experience during loan spells at Coventry, Newcastle and Leicester in recent seasons.
He ended the current campaign on loan with the Foxes and made 12 appearances for the Championship side managed by Sven-Goran Eriksson.
Chelsea left-back Patrick van Aanholt has signed a new four-year contract with the Stamford Bridge club.