A group III nitride crystal substrate is provided, wherein, a uniform distortion at a surface layer of the crystal substrate is equal to or lower than 1.7×10−3, and wherein a plane orientation of the main surface has an inclination angle equal to or greater than −10° and equal to or smaller than 10° in a [0001] direction with respect to a plane including a c axis of the crystal substrate. A group III nitride crystal substrate suitable for manufacturing a light emitting device with a blue shift of an emission suppressed, an epilayer-containing group III nitride crystal substrate, a semiconductor device and a method of manufacturing the same can thereby be provided.