There is provided a nitride semiconductor device with low leakage current and high efficiency in which, while a zinc oxide based compound such as MgxZn1-xO (0≦x≦0.5) is used for a substrate, crystallinity of nitride semiconductor grown thereon is improved and film separation or cracks are prevented. The nitride semiconductor device is formed by laminating nitride semiconductor layers on a substrate (1) made of a zinc oxide based compound such as MgxZn1-xO (0≦x≦0.5). The nitride semiconductor layers include a first nitride semiconductor layer (2) made of AlyGa1-yN (0.05≦y≦0.2) which is provided in contact with the substrate (1), and nitride semiconductor layers (3) to (5) laminated on the first nitride semiconductor layer (2) so as to form a semiconductor element.