A method for manufacturing a semiconductor device is provided. The method for manufacturing a semiconductor device comprises providing a first substrate including a buffer layer and a base substrate, forming a stacked mold structure including a plurality of unit laminates on the buffer layer, each of the unit laminates including a first sacrificial layer, a first silicon layer, a second sacrificial layer, and a second silicon layer sequentially stacked in a vertical direction and replacing the stacked mold structure with a stacked memory structure through a replacement process, wherein the stacked memory structure includes a metal pattern which replaces the first sacrificial layer and the second sacrificial layer, and an insulating pattern which replaces the second silicon layer, the buffer layer includes silicon-germanium, and a germanium concentration of the buffer layer varies depending on the germanium concentration of the first sacrificial layer and the germanium concentration of the second sacrificial layer.