Toward making available III nitride crystal substrates advantageously employed in light-emitting devices, and light-emitting devices incorporating the substrates and methods of manufacturing the light-emitting devices, a III nitride crystal substrate has a major face whose surface area is not less than 10 cm2 and, in a major-face principal region excluding the peripheral margin of the major face from its outer periphery to a 5 mm separation from its outer periphery, the total dislocation density is from 1×104 cm−2 to 3×106 cm−2, and the ratio of screw-dislocation density to the total dislocation density is 0.5 or greater.