A semiconductor device comprises MOS transistors sequentially arranged in the plane direction of a substrate, wherein a gate electrode and a wiring portion for connecting between the gate electrodes to each other are implanted into a layer that is lower than a surface of the substrate in which a diffusion layer has been formed. A first device isolation area with a STI structure for separating the diffusion layers that function as a source/drain area is formed on the surface of the substrate. A second device isolation area with the STI structure for separating channel areas of the MOS transistors adjacent to each other is formed in a layer that is lower than a layer that has the first device isolation area.