Abstract
The present disclosure provides a semiconductor device and a fabrication method thereof. The semiconductor device includes a first nitride semiconductor layer, a second nitride semiconductor layer, a gate structure, a first spacer and a second spacer. The second nitride semiconductor layer is formed on the first nitride semiconductor layer and having a greater bandgap than that of the first nitride semiconductor layer. The gate structure is disposed on the second nitride semiconductor layer. The first spacer is disposed on the second nitride semiconductor layer. The in second spacer is disposed on the second nitride semiconductor layer and spaced apart from the first spacer by the gate structure. The bottom of the first spacer has a first width, the bottom of the second spacer has a second width, and the first width is different from the second width.