In a stacking semiconductor device in which a first-layer and a second-layer semiconductor devices are stacked and bonded with a solder, warpage occurs due to a difference in thermal expansion coefficient of constituent members or a difference in elastic modulus of individual members. Therefore, between the first-layer and the second-layer semiconductor devices are provided an external connection terminal of solder and a thermosetting resin, and the stacking semiconductor device is heated at 150 to 180° C., which are the temperatures of preheating for reflow of the solder, for 30 to 90 seconds. Thereby the warpage of the first-layer semiconductor device is reduced and the thermosetting resin is cured completely in this state. Then, the temperature is raised to a reflow temperature of the solder and solder bonding using the external connection terminal is performed. Thereby, the bonding reliability of a solder-bonded portion of the stacking semiconductor device is considerably improved.