A method of manufacturing a semiconductor device includes forming a dummy gate structure on a substrate, partially removing the dummy gate structure to form a first opening that divides the dummy gate structure, forming a first division pattern structure in the first opening, replacing the dummy gate structure with a gate structure, removing the first division pattern structure to form a second opening, removing a portion of the gate structure from a sidewall of the second opening to enlarge the second opening, and forming a second division pattern in the enlarged second opening.