To solve the problem of a conventional board mounted semiconductor device such that the heat conductivity drops and the electric properties deteriorate due to its structure and material property.

This semiconductor device has an anisotropic wiring board 20 which is made by packing a plurality of conductive materials whose surfaces are covered and insulated into a bundle and bonding it with an insulating adhesive, and slicing it. A semiconductor element 22 is mounted on the board, it is connected with an electrode pad 19a on the board by connecting material 23, and the surrounding is sealed with sealing resin 24, thus constituting this semiconductor device therefore, the electric resistance between the top and bottom of the substrate and the inductance become remarkably small, and the semiconductor device which is excellent electrically and thermally can be materialized.