According to one embodiment, a nitride semiconductor device includes a first, a second, a third and a fourth transistor of n-type channel and a resistor. The first transistor has a first gate, a first source, and a first drain. The second transistor has a second gate, a second source electrically connected to the first gate, and a second drain. The third transistor has a third gate, a third source electrically connected to the first source, and a third drain electrically connected to the first gate and the second source. The fourth transistor has a fourth gate electrically connected to the third gate, a fourth source electrically connected to the first source and the third source, and a fourth drain electrically connected to the second gate. The resistor has one end electrically connected to the second drain and one other end electrically connected to the second gate and the fourth drain.