An electrical connection inside a semiconductor device is established by lead frames formed of plural conductor plates. The lead frames are disposed three-dimensionally so that the respective weld parts thereof are exposed toward a laser light source used in the laser welding. The laser welding is then performed by irradiating a laser beam. According to the above, welding can be performed readily in a reliable manner. The productivity of the semiconductor device and the manufacturing method of the semiconductor device can be thus enhanced. In addition, because the lead frames have the cooling effect, they have the capability of a heat spreader. It is thus possible to provide a semiconductor device and a manufacturing method of the semiconductor device with high productivity.