A method of fabricating a transistor of a semiconductor device comprises: forming a gate in a NMOS region and a PMOS region of a semiconductor substrate; forming a gate spacer on a sidewall of the gate; performing an ion implantation process on the NMOS region to form a junction region in the NMOS region; depositing an oxide film on the entire surface of the semiconductor substrate including the gate; removing hydrogen (H) existing in the oxide film and the gate spacer; and removing the oxide film in the PMOS region and performing a ion implantation process on the PMOS region to form a junction region in the PMOS region.