PURPOSE: To contrive the improvement of the reliability of an oxide film, which is formed on the surfaces of diffused layers, and a reduction in a program voltage in a one-layer polycrystalline silicon FLOTOX type EEPROM.

CONSTITUTION: The impurity concentration in the surfaces of diffused layers, in which a control gate part 3c and a drain part 3b of a MOS transistor are respectively formed, is made lower than that in the surfaces of conventional diffused layers to improve the reliability of an oxide film, which is formed on the surfaces of the diffused layers, the impurity concentration in the interiors of the diffused layers is set into an impurity concentration of a value equal with the peak value or higher of the impurity concentration in the conventional diffused layers and a program voltage is made low.