A method of fabricating a semiconductor device is provided. A sacrificial gate, a hard mask, a spacer and a first interlayer insulating film are formed on a substrate. The hard mask, a part of the spacer, and a part of the first interlayer insulating film are removed to expose an upper portion of the sacrificial gate. A sacrificial insulating layer covers the exposed upper portion of the sacrificial gate. A second interlayer insulating film covers the sacrificial insulating layer, the spacer and the first interlayer insulating film. The sacrificial insulating layer and the second interlayer insulating film are partially removed to expose a top surface of the sacrificial gate. The sacrificial gate and the sacrificial insulating layer are removed to form a trench. A gate structure is formed in the trench.