A method for fabricating a semiconductor device includes forming a dielectric film containing a porogen material above a substrate; removing a portion of the porogen material contained in the dielectric film so as to make a concentration of the porogen material higher in a part on a lower side of the dielectric film than in another part on a higher side of the dielectric film; forming an opening halfway in the dielectric film from which a portion of the porogen material has been removed to leave the dielectric film below a bottom of the opening; removing or polymerizing a remainder of the porogen material contained in the dielectric film; and etching the bottom of the opening after removing or polymerizing the remainder of the porogen material.