in the disclosed method for manufacturing a semiconductor module , a metal layer and a cooler , which have different coefficients of thermal expansion from each other , are joined into a single unit via an insulating resin sheet . a work , comprising a semiconductor element placed on the metal layer with solder interposed therebetween , is fed into a reflow furnace . the work , in that state , is heated in the reflow furnace , thereby mounting the semiconductor element to the metal layer . the heating is carried out such that the temperature of the cooler and the temperature of the metal layer differ by an amount that make the cooler and the metal layer undergo the same amount of thermal expansion as each other .