A method for manufacturing a semiconductor device and a semiconductor device, the method including forming an active pattern on a substrate such that the active pattern includes sacrificial patterns and semiconductor patterns alternately and repeatedly stacked on the substrate; and forming first spacer patterns at both sides of each of the sacrificial patterns by performing an oxidation process, wherein the first spacer patterns correspond to oxidized portions of each of the sacrificial patterns, wherein the sacrificial patterns include a first semiconductor material containing impurities, wherein the semiconductor patterns include a second semiconductor material different from the first semiconductor material, and wherein the impurities include an element different from semiconductor elements of the first semiconductor material and the second semiconductor material.