A reduction of a resistance of a bit line of a memory cell array and a reduction of a forming area of the memory cell array are planed. Respective bit lines running at right angles to a word line are composed of a diffusion bit line formed in a semiconductor substrate and a linear metal bit line on an upper side of the diffusion bit line. The diffusion bit line is formed in a linear pattern on a lower side of the metal bit line in the same manner, and the metal bit line is connected with the diffusion bit line between the word lines. An interlayer insulating film is formed on the memory cell array, and the metal bit line is formed with being buried in it.