The device includes: a tunnel insulating layer, a charge trap layer; a blocking insulating layer; and a gate electrode sequentially formed on a substrate. The charge trap layer includes: plural trap layers comprising a first material having a first band gap energy level; spaced apart nanodots, each nanodot being at least partially surrounded by at least one of the trap layers, wherein the nanodots comprise a second material having a second band gap energy level that is lower than the first band gap energy level; and an intermediate blocking layer comprising a third material having a third band gap energy level that is higher than the first band gap energy level, formed between at least two of the trap layers. This structure prevents loss of charges from the charge trap layer and improves charge storage capacity.