Method of manufacturing semiconductor device

A method for manufacturing a semiconductor device comprising a nonvolatile memory transistor of a stacked gate structure having a floating gate and a control gate, and a MOS transistor of a single gate structure, said method comprising:

• forming a first insulation film on a semiconductor substrate, said first insulation film becoming a gate oxide film of both the nonvolatile memory transistor and the MOS transistor;
• forming a first conductive layer on the first insulation film;
• removing the first conductive layer in an area extending in a direction perpendicular to a direction in which the control gate is formed extendedly from the first conductive layer to form a region for separating the floating gate;
• forming a second insulation layer on the first conductive layer;
• forming a second conductive layer so as to form the control gate;
• patterning the second conductive layer on the second insulation film;
• and
• patterning the first conductive layer to form the stacked gate structure and the single gate structure,
• wherein the MOS transistor of the single gate structure includes a high-voltage transistor and forming a peripheral circuit, and
• wherein the step of forming the first insulation film comprises the steps of forming a gate insulation film of the high-voltage transistor, and forming a tunnel oxide film between the floating gate and the substrate and simultaneously forming a gate insulation film of the MOS transistor forming the peripheral circuit.