The embodiments of the present disclosure provide a semiconductor device. The semiconductor device includes a first III-V compound layer disposed over a substrate and a second III-V compound layer disposed over the first III-V compound layer, wherein a first carrier channel is formed in the interface between the first III-V compound layer and the second III-V compound layer. The semiconductor device also includes a third III-V compound layer disposed over the second III-V compound layer and a fourth III-V compound layer disposed over the third III-V compound layer, wherein a second carrier channel is formed in an interface between the third III-V compound layer and the fourth III-V compound layer. The semiconductor device includes a gate structure and S/D regions disposed on two opposite sides of the gate structure, wherein the first carrier channel and the second carrier channel are extended between the S/D regions.