Abstract: The semiconductor package and manufacturing method thereof whereby the inexpensive package of high thermal conductivity is obtained by applying a Cu/Mo/Cu clad material for a base plate which matches the thermal expansion of a semiconductor chip, and the inexpensive package with high heat transfer suitable for a high frequency device is obtained by controlling a thickness of glass, and a size of a lead (width, thickness), thereby to match impedance of a wiring portion with that of the semiconductor chip, by plating only necessary areas with Au, and by plating the exterior with Sn.