A method for fabricating a semiconductor device, including forming a lower structure on a substrate. The lower structure includes a first sacrificial layer and a first insulating layer alternately and repeatedly stacked. A first hole is formed in the lower substrate. The first hole exposes an upper surface of the substrate. A sacrificial pattern is formed in the first hole. A porosity of the sacrificial pattern increases toward the substrate. An upper structure is formed on the lower structure and the sacrificial pattern. The upper structure includes a second sacrificial layer and a second insulating layer alternatively and repeatedly stacked. A second hole is formed in the upper structure. The second hole exposes the sacrificial pattern. The sacrificial pattern is removed.