The reliability of a semiconductor device having an embedded wire in the lowest layer wire is improved. In a main surface of a semiconductor substrate, MISFETs are formed and over the main surface, insulating films 10, 11 are formed. In the insulating films 10, 11 a contact hole is formed and a plug is embedded therein. Over the insulating film 11 in which the plug is embedded, insulating films 14, 15, 16 are formed and an opening is formed in the insulating films 14, 15, 16 and a wire is embedded therein. The insulating film 15 is an etching stopper film when etching the insulating film 16 in order to form the opening, containing silicon and carbon. The insulating film 11 has a high hygroscopicity and the insulating film 15 has a low moisture resistance, however, by interposing the insulating film 14 therebetween and making the insulating film 14 have a higher density of the number of Si (silicon) atoms than that of the insulating film 11 , an electrically weak interface is preventedfrom being formed.