A semiconductor device is a resin package structure including a semiconductor element T1 molded with a first resin 6. The first resin 6 contains a filler 7 including an electrical insulating capsule enclosed with a phase-change-material that absorbs ambient heat and phase-changes so as to increase a dielectric-strength. The effect of the filler 7 achieves a structure with satisfactory heat dissipation and a high withstand voltage.