A nitride semiconductor substrate that is constituted by a single crystal of a group III nitride semiconductor and includes a main surface for which the closest low index crystal plane is a (0001) plane includes an inclined interface growth region that has grown with inclined interfaces other than the (0001) plane serving as growth surfaces. A ratio of an area occupied by the inclined interface growth region in the main surface is 80% or more. When a dislocation density is determined based on a dark spot density by observing the main surface in a field of view that is 250 μm square using a multiphoton excitation microscope, the main surface does not include a region that has a dislocation density higher than 3×106 cm−2, and the main surface includes dislocation-free regions that are 50 μm square and do not overlap each other, at a density of 100 regions/cm2 or more.