Abstract: A nitride-based semiconductor device includes a first and second nitride-based semiconductor layers, two or more source/drain (S/D) electrodes, a gate electrode, a doped III-V semiconductor layer, a gate protection layer and a first passivation layer. The doped III-V semiconductor layer is disposed between the second nitride-based semiconductor layer and the gate electrode. The gate protection layer caps the gate electrode and the doped III-V semiconductor layer and is separated from the S/D electrodes. The first passivation layer covers the second nitride-based semiconductor layer and the gate protection layer and abuts against sidewalls of the S/D electrodes which are separated from the gate protection layer by the first passivation layer.