A semiconductor device includes a stack and a plurality of memory strings. The stack is formed on a substrate, and the stack includes conductive layers and insulating layers alternately stacked. The memory strings penetrate the stack along a first direction. Each of the memory strings includes a first conductive pillar, a second conductive pillar, a channel layer and a memory structure. The first conductive pillar and the second conductive pillar extend along the first direction, respectively, and electrically isolated to each other. The channel layer extends along the first direction. The channel layer is disposed between the first conductive pillar and the second conductive pillar, and the channel layer is coupled to the first conductive pillar and the second conductive pillar. The memory structure surrounds the first conductive pillar, the second conductive pillar and the channel layer.