The semiconductor device according to the present invention comprises a V-groove having V-shaped cross-section formed on a semiconductor substrate or on an epitaxial growth layer grown on a semiconductor substrate, and an active layer is provided only at the bottom of said V-groove. The method for manufacturing a semiconductor device according to the present invention comprises the steps of forming a stripe-like etching protective film in direction of a semiconductor substrate or an epitaxial growth layer grown on it, performing gas etching using hydrogen chloride as etching gas on a semiconductor substrate or on an epitaxial growth layer grown on a semiconductor substrate to form a V-groove, and forming an active layer at the bottom of said V-groove.