A semiconductor device includes a conductive substrate, a channel forming layer, a first electrode, and a second electrode. The channel forming layer is located above the conductive substrate and includes at least one hetero-junction structure. The hetero-junction structure includes a first GaN-type semiconductor layer providing a drift region and a second GaN-type semiconductor layer having a bandgap energy greater than the first GaN-type semiconductor layer. A total fixed charge quantity of charges in the first GaN-type layer and the second GaN-type layer is from 0.5×1013 to 1.5×1013 cm−2. The charges in the first GaN-type layer and the second GaN-type layer include charges generated by the polarization in the first GaN-type layer. Accordingly, the semiconductor device capable of improving a break-down voltage and decreasing an on-resistance is obtained.