A method of fabricating a semiconductor device is disclosed comprising the steps of: providing a substrate having a first region, a second region and a plurality of gate electrodes which are formed on the first and second regions of the substrate; forming a mask film to expose the first region of the substrate while covering the second region of the substrate, such that the mask film has a negative lateral profile at a boundary between the first and second regions of the substrate; forming sigma trenches in the first region of the substrate by etching the first region of the substrate using the mask film and the gate electrodes as a mask; and forming an epitaxial layer in each of the sigma trenches.