Provided is a nitride semiconductor device 3 including a GaN electron transit layer 13, an AlGaN electron supply layer 14 in contact with the electron transit layer 13, a gate layer 15, formed selectively on the electron supply layer 14 and constituted of a nitride semiconductor composition effectively not containing an acceptor type impurity, and a gate electrode 16, formed on the gate lever 15, and satisfying the following formula (1): d G ⁢ 2 ⁢ E F ⁢ q ⁡ ( N DA + N A - N DD - N D ) ɛ 0 ⁢ ɛ C + Φ B - d B ⁢ P ɛ 0 ⁢ ɛ B > 0 ( 1 )