Similar to the contact plug 8 a described with reference to FIG. 10, a contact plug 5 a made of conductive material such as W is formed in the contact hole 4A. Similar to the wiring layer 9 a and pad layer 9 b described with reference to FIG. 10, a second-level wiring layer 6 a and a second-level pad layer 6 b are formed on the insulating film 4.