A nitride semiconductor free-standing substrate includes a nitride semiconductor crystal and an inversion domain with a density of not less than 10/cm2 and not more than 600/cm2 in a section parallel to a surface of the substrate and inside the substrate. A method for making the nitride semiconductor free-standing substrate includes a nitride semiconductor crystal growth step of growing on a heterosubstrate a nitride semiconductor crystal including an inversion domain with a density of not less than 10/cm2 and not more than 600/cm2 by adjusting a growth condition at an initial growth stage of the nitride semiconductor crystal, and a separation step for separating the grown nitride semiconductor crystal from the heterosubstrate to form the nitride semiconductor free-standing substrate.