The memory device includes a first tunnel insulation layer pattern on a semiconductor substrate, a second tunnel insulation layer pattern having an energy band gap lower than that of the first tunnel insulation layer pattern on the first tunnel insulation layer pattern, a charge trapping layer pattern on the second tunnel insulation layer pattern, a blocking layer pattern on the charge trapping layer pattern, and a gate electrode on the blocking layer pattern. The memory device further includes a source/drain region at an upper portion of the semiconductor substrate. The upper portion of the semiconductor substrate is adjacent to the first tunnel insulation layer pattern.