a substrate;

a nonvolatile memory device formed in a memory cell region of said substrate and having a multilayer gate electrode structure comprising a tunnel insulating film covering said substrate and a floating gate electrode formed on the tunnel insulating film and having sidewall surfaces covered with a protection insulating film formed of a thermal oxide film;

a semiconductor device formed in a device region of said substrate, the semiconductor device comprising a gate insulating film covering said substrate and gate electrode formed on the gate insulating film;

wherein a bird's beak structure is formed of a thermal oxide film at an interface of the tunnel insulating film and the floating gate electrode, the bird's beak structure penetrating into the floating gate electrode along the interface from the sidewall faces of the floating gate electrode;

the gate insulating film is interposed between said substrate and the gate electrode to have a uniform thickness at the region under the entire gate electrode;

wherein the bird's beak structure is the same thermal oxide film as the protective insulating film;

wherein the protection insulating film continuously covers sidewall faces and a top surface of the multilayer gate electrode structure; wherein the protection insulating film covers the multilayer gate electrode uniformly and sidewalls are formed over the protection insulating film, said sidewalls covering the entire side surface of the multilayer gate electrode structure;

and the multilayer gate electrode structure, including a control gate has a substantially uniform width.