a semiconductor device includes a two - input nor circuit including four mos transistors arranged in a line . each of the mos transistors is disposed on a planar silicon layer disposed on a substrate . the drain , gate , and source of the mos transistor are arranged in the vertical direction . the gate surrounds a silicon pillar . the planar silicon layer is constituted by a first activation region of a first conductivity type and a second activation region of a second conductivity type . the first and second activation regions are connected to each other via a silicon layer disposed on a surface of the planar silicon layer , so as to form a nor circuit having a small area .