A semiconductor device is capable of being applied with both a positive and a negative voltage to its control gate, and writing to its memory requires a low voltage. A control gate is formed on a memory unit region of a field oxide film, and an inter-layer silicon oxide film is formed on its surface. A gate oxide film for a non-volatile memory is formed on a P substrate between N type diffusion layers. The floating gate is formed on the inter-layer silicon oxide film, the field oxide film, and the gate oxide film for the non-volatile memory. Since a large coupling ratio between the control gate and the floating gate is available on the field oxide film, memory rewriting requires only a low voltage. Further, since the control gate is formed by a poly silicon film, both a positive voltage and a negative voltage can be applied to the control gate.