An embodiment of the present invention relates to a method of manufacturing a flash memory device. The method includes sequentially forming a tunnel oxide film, an oxide film, and a first conductive layer on a semiconductor substrate, infiltrating a first etchant between grains of the first conductive layer to form a plurality of nano-crystal points in the oxide film, removing the first conductive layer using a second etchant, wherein during the process of removing the first conductive layer, portions of the nano-crystal points of the oxide film are removed by the second etchant, thereby forming a plurality of nano-crystal formation holes in the oxide film, filling the plurality of holes with a non-conductive layer to form a plurality of nano-crystals respectively having an isolated shape, sequentially forming a dielectric layer and a second conductive layer on the oxide film including the plurality of nano-crystals, and sequentially patterning the second conductive layer, the dielectric layer, the oxide film including the nano-crystals, and the tunnel oxide film.