A substrate processing apparatus including an electrostatic chuck on which a substrate is mountable; a ring surrounding the electrostatic chuck, the ring including a first coupling groove; and a first floating electrode in the first coupling groove of the ring, the first floating electrode having a ring shape, wherein a top surface of the first floating electrode is exposed at the ring, and the first floating electrode has a tapered shape including an inclined surface that is inclined in a downward direction toward the electrostatic chuck.