A semiconductor device including memory cells that are three-dimensionally arranged is provided. The semiconductor device includes: a stack structure including first and second layers, which are sequentially stacked on a substrate, the first layer including first and second semiconductor patterns, which are spaced apart from each other and extend in a first direction, and a first bitline, which extends in a second direction different from the first direction and is electrically connected to the first and second semiconductor patterns, the second layer including third and fourth semiconductor patterns, which are spaced apart from each other and extend in the first direction, and a second bitline, which extends in the second direction and is electrically connected to the third and fourth semiconductor patterns, and each of the first through fourth semiconductor patterns including a source, a channel, a drain, and a bottom electrode; a first wordline connecting the channels of the first and third semiconductor patterns in a vertical direction; a second wordline connecting the channels of the second and fourth semiconductor patterns in the vertical direction.