A flash memory device according to the present invention includes a semiconductor fin including a top surface and a side surface originated from different crystal planes. The flash memory device comprises: insulating layers having different thicknesses formed on a side surface and a top surface of the semiconductor fin, a storage electrode, a gate insulating layer and a control gate electrode sequentially formed on the insulating layers. A thin insulating layer enables charges to be injected or emitted through it, and a thick insulating layer increases a coupling ratio. Accordingly, it is possible to increase an efficiency of a programming or an erase operation of a flash memory device.