A method of fabricating a semiconductor device includes forming a plurality of mask patterns comprising a real mask pattern and a dummy mask pattern on a substrate, removing the dummy mask pattern and etching the substrate using the real mask pattern as a mask to form a first trench, a second trench, and a fin-type pattern defined by the first trench and the second trench. The second trench contacting the fin-type pattern comprises a smooth pattern which is convex and positioned between a bottom surface and a side surface of the second trench, a first concave portion which is positioned between the side surface of the second trench and the smooth pattern, and a second concave portion which is positioned between the convex portion and the bottom surface of the second trench.