A parallel structure comprising source/drain and channel layers alternately stacked on a substrate, and gate stacks formed around peripheries of the channel layers. Each of the channel layers, the source/drain layers on upper and lower sides of the channel layer, and the gate stack formed around the channel layer, form a semiconductor device. In each semiconductor device, one of the source/drain layers is in contact with a first electrically-conductive channel disposed on an outer periphery of the active region, the other is in contact with a second electrically-conductive channel on the outer periphery of the active region, and the gate stack is in contact with a third electrically-conductive channel disposed on the outer periphery of the active region. The first electrically-conductive channel is common to the semiconductor devices, the second electrically-conductive channel is common to the semiconductor devices, and the third electronically-conductive channel is common to the semiconductor devices.