A method of fabricating a semiconductor device is disclosed. The method includes forming an active pattern protruding orthogonally from a substrate; forming a preliminary gate structure on the active pattern to cross the active pattern; etching the active pattern to form preliminary recess regions at both sides of the preliminary gate structure, wherein each of the preliminary recess regions is formed to define a delta region in an upper portion of the active pattern; forming a sacrificial layer on inner side surfaces and a bottom surface of the active pattern exposed by each of the preliminary recess regions; etching the delta regions and the sacrificial layer to form recess regions having a ‘U’-shaped section; and forming source/drain regions in the recess regions.