PURPOSE: To obtain a constitution in which the effect of hot carriers is less and soft writing is suppressed in a floating gate type memory device, by decreasing the impurity concentration of an impurity region, which is formed beneath a gate insulating film wherein at least writing is performed, in comparison with the impurity concentration in another impurity region.

CONSTITUTION: A tunnel oxide film 7 is formed not on a high concentration region 17 of a drain region 14 but on a low concentration region 5. The low concentration region 5 serves the role of an offset part 18 of the drain region in this structure, Namely, only the side of the drain region 14 has an LDD structure. (When the xj (diffusion depth) of the N- region 5 is deeper than the N+ region 17, the DDD (Double Diffused Drain) structure is obtained.) Therefore the electric field intensity in the tunnel gate oxide film 7, wherein writing is carried out, is alleviated. As a result, a memory device 16, in which the effect of hot carriers is less and soft writing is suppressed, is obtained. When the tunnel gate oxide film 7 is formed on the N- region 5 as a thermal oxide film, the quality of the film becomes excellent and reliability is improved.