A stacked semiconductor device and a method for fabricating the stacked semiconductor device are disclosed. The stacked semiconductor device includes a first insulating interlayer having an opening that partially exposes a substrate, wherein the substrate includes single crystalline silicon, and a first seed pattern that fills the opening, wherein the first seed pattern has an upper portion disposed over the opening, and the upper portion is tapered away from the substrate. The stacked semiconductor device further includes a second insulating interlayer formed on the first insulating interlayer, wherein a trench that exposes the upper portion of the first seed pattern penetrates the second insulating interlayer, and a first single crystalline silicon structure that fills the trench.