In some embodiments, a semiconductor device and a fabricating method thereof are provided. The method can comprise: providing a semiconductor substrate; forming a gate structure on the semiconductor substrate; forming an epitaxial substrate layer on the semiconductor substrate on both sides of the gate structure; forming a hard mask layer conformally covering the epitaxial substrate layer, the gate structure and the semiconductor substrate; etching the hard mask layer to form a hard mask sidewall layer on sidewall surfaces of the gate structure and on the epitaxial substrate layer; using the hard mask sidewall layer as a mask to etch the epitaxial substrate layer and the semiconductor substrate to form trenches on both sides of the gate structure; and forming a stress layer in the trenches.