A nitride semiconductor device includes: a substrate containing Si; a channel layer provided on the substrate and made of nitride semiconductor material; a barrier layer provided on the channel layer and made of nitride semiconductor material; a first and second main electrode connected to the barrier layer; and a control electrode provided between the first main electrode and the second main electrode on the barrier layer. The substrate includes at least one layer having a resistivity of 1 kΩ/cm or more.