One semiconductor device includes one parallel transistor for connecting in parallel multiple vertical transistors disposed in an active region on a semiconductor substrate. The parallel transistor includes semiconductor pillars that project out in a direction perpendicular to a main surface of the semiconductor substrate; a lower diffusion layer that is disposed below the semiconductor pillars; upper diffusion layers that are each disposed on an upper section of the semiconductor pillars; and gate electrodes disposed, with a gate insulator film therebetween, on the entire side surfaces of the semiconductor pillars. The upper diffusion layers are connected to one upper contact plug that is disposed over the upper diffusion layers.