Manufacturing technique for an IC device which includes forming the first conductor film over a memory cell forming region and over a peripheral circuit forming region of a semiconductor substrate, patterning the first conductive film lying over the memory cell forming region to form a first conductive pattern which serves as a first or control gate electrode of a memory cell and leaving the first conductive film over the peripheral circuit forming region, forming a second conductive film over both the memory cell forming region and the first conductive film in the peripheral circuit forming region, etching the second conductive film to form a second or memory gate electrode of the memory cell on at least a side wall of the first conductive pattern, and followed by the formation of a gate electrode of a peripheral circuit transistor by etching the first conductive film in the peripheral circuit forming region.