Abstract
A nitride-based semiconductor device includes a first nitride-based semiconductor layer, a second nitride-based semiconductor layer, a first conductive layer, a second conductive layer, and a gate electrode. The second nitride-based semiconductor layer is disposed over the first nitride-based semiconductor layer and has a bandgap greater than a bandgap of the first nitride-based semiconductor layer. The first conductive layer is disposed over the second nitride-based semiconductor layer and has a top surface and a plurality of recesses at the top surface. The second conductive layer at least fills into the recesses, in which the first conductive layer comprises at least one first element excluded in the second conductive layer. The gate electrode is disposed over the first conductive layer and the second conductive layer.