PURPOSE: To provide a method of manufacturing a semiconductor package stem, wherein a heat sink can be enhanced enough in position accuracy without an after process (flatting process).

CONSTITUTION: A semiconductor package stem is formed through such a manner that a block-shaped heat sink 12 mounted with a semiconductor chip is disposed upright on an eyelet main body 11, wherein a clad material 10 composed of a fist material used for an eyelet main body 11 and a second material used for the heat sink 12 which are bonded together in layer is prepared, and the clad material 10 is press-molded into an integral structure composed of the heat sink 12 and the eyelet main body 11. Or, a third material suitable for resistance welding is laminated on the second material for the formation of the clad material 10.