A semiconductor device includes: a semiconductor region; a plurality of bit line diffusion layers formed in an upper portion of the semiconductor region and each extending in a row direction; a plurality of bit line insulating films formed on the bit line diffusion layers; a plurality of gate insulting films formed between the respective adjacent bit line diffusion layers on the semiconductor region; and a plurality of word lines each formed on the semiconductor region in a column direction and each intersecting with the bit line insulating films and the gate insulating films. Memory cells are formed at intersections of the gate insulating films and the word lines. A plurality of connection diffusion layers including connection parts electrically connected to the bit line diffusion layers are formed in the upper portion of the semiconductor region, and a level of upper faces of the connection parts is lower than a level of upper faces of the connection diffusion layers in the semiconductor region.