A GaN crystal substrate is provided, which has a diameter of not less than 20 mm and a thickness of not less than 70 μm and not more than 450 μm, and has a light absorption coefficient of not less than 7 cm−1 and not more than 68 cm−1 for light in the wavelength range of not less than 375 nm and not more than 500 nm. A fabricating method of the GaN crystal substrate, and a light-emitting device fabricated using the GaN crystal substrate are also provided.