High-electron mobility transistor and fabrication method thereof

A high-electron mobility transistor includes a substrate; a buffer layer on the substrate; a AlGaN layer on the buffer layer; a passivation layer on the AlGaN layer; a source region and a drain region on the AlGaN layer; a source layer and a drain layer on the AlGaN layer within the source region and the drain region, respectively; a gate on the AlGaN layer between the source region and a drain region; and a field plate on the gate and the passivation layer. The field plate includes an extension portion that laterally extends to an area between the gate and the drain region. The extension portion has a wave-shaped bottom surface.