Abstract: A nitride-based semiconductor device includes a first nitride-based semiconductor layer, a second nitride-based semiconductor layer, a first nitride-based transistor, a second nitride-based transistor, and a thermal resistor. The first nitride-based transistor is disposed over the second nitride-based semiconductor layer and applies the 2DEG region as an own channel. The second nitride-based transistor is disposed over the second nitride-based semiconductor layer and applying the 2DEG region as an own channel. The temperature sensor is disposed over the second nitride-based semiconductor layer and between first and second nitride-based transistors. The temperature sensor is in a strip shape and at least turns twice in a region between first and second nitride-based transistors.