A semiconductor device and a method for manufacturing the semiconductor device is disclosed. The semiconductor device includes a bit line formed to extend into a semiconductor substrate, a charge storage layer formed on the semiconductor substrate, a word line formed above the charge storage layer to extend across the bit line, a gate electrode formed on the charge storage layer under the word line and between bit lines, a first insulating film formed over the bit line and to extend in the direction of the bit line and a second insulating film that includes a different material than that of the first insulating film and formed to adjoin a side surface of the first insulating film. In addition, the semiconductor device includes an interlayer insulating film that includes a different material from that of the second insulating film that is formed on the first insulating film and the second insulating film and a contact plug coupled to the bit line and formed to penetrate through the first insulating film and the interlayer insulating film and to be sandwiched by the second insulating film.