To achieve a higher operating speed, higher reliability, and lower power consumption by reducing the thickness of an inter-poly silicon insulator film between a floating gate and a control gate of a flash memory, a silicon dioxide film, a silicon nitride film, tantalum pentoxide, and a silicon dioxide film are formed in a multilayer structure to serve as the inter-poly insulator film between a floating gate and a control gate. With this configuration, tantalum pentoxide formed on the silicon nitride film has a dielectric constant of 50 or more, which is higher than that of the silicon dioxide film, and the thickness of the inter-poly silicon insulator film can be reduced.