PURPOSE: To prevent a reduction in heat radiation efficiency due to air bubbles inside solder and a stress for an element, by a method wherein a semiconductor element is mounted on a lower jig, and a heat sink is mounted on the semiconductor element through solder, and after they are positioned by an upper jig, the semiconductor element and heat skin are soldered by heating.

CONSTITUTION: A semiconductor element 2 in which a soldered plate is put upwardly is inserted into a recess 11 of a lower jig 1 and a solder pellet 3 is mounted thereon followed by mounting of a heat sink 4, and they are positioned by a jig 5 and fixed. Such an assembly is conveyed on a belt conveyor at an electric furnace and passes though the electric furnace, and is heated to melt the solder pellet 3 to connect the semiconductor element with the heat sink 4. After it comes out of the electric furnace, the jig 5 is removed to take it out from the jig 1. Thus, as air bubbles left inside solder can be expelled through its own weight of the heat skin, it is possible to bond the heat sink stably to semiconductor element while suppressing the deterioration of heat radiation properties due to air bubbles and heat stress.