Priorly, semiconductor devices wherein a flexible sheet with a conductive pattern was employed as a supporting substrate, a semiconductor element was mounted thereon, and the ensemble was molded have been developed. In this case, problems occur that a multilayer wiring structure cannot be formed and warping of the insulating resin sheet in the manufacturing process is prominent. In order to solve these problems, a laminated plate 10 in which a thin first conductive film 11 and a thick second conductive film 12 have been laminated via a third conductive film 13 is used. After forming a conductive pattern layer 11A of a fine pattern by etching the thin first conductive film 11, anchor portions 15 are formed by overetching the third conductive film 13 by use of the conductive pattern layer 11A as a mask, and an insulating adhesive layer 16 and a sealing resin layer 22 are made to bite into the anchor portions 15 so as to strengthen bonding of the insulating adhesive layer 16 and sealing resin layer 22 with the conductive pattern 11A.