A charge holding insulating film in a memory cell is constituted by a laminated film composed of a bottom insulating film, a charge storage film, and a top insulating film on a semiconductor substrate. Further, by performing a plasma nitriding treatment to the bottom insulating film, a nitride region whose nitrogen concentration has a peak value and is 1 atom % or more is formed on the upper surface side in the bottom insulating film. The thickness of the nitride region is set to 0.5 nm or more and 1.5 nm or less, and the peak value of nitrogen concentration is set to 5 atom % or more and 40 atom % or less, and a position of the peak value of nitrogen concentration is set within 2 nm from the upper surface of the bottom insulating film, thereby suppressing an interaction between the bottom insulating film and the charge storage film.