Abstract: Disclosed herein is a flash memory device in which the distribution of threshold voltage is significantly reduced and the durability is improved even though a floating gate has a micro- or nano-size length. It comprises a tunneling insulation film formed on a semiconductor substrate; a multilayer floating gate structure comprising a first thin storage electrode, a second thick storage electrode, and a third thin storage electrode, defined in that order on the tunneling insulation film; an interelectrode insulation film and a control electrode formed in that order on the floating gate structure; and a source/drain provided in the semiconductor substrate below the opposite sidewalls of the floating gate structure. The novel flash memory device can be readily fabricated at a high yield through a process compatible with a conventional one.