The present invention provides a Group III nitride semiconductor light-emitting device exhibiting improved emission performance. In a MQW structure light-emitting layer in which a plurality of layer units is repeatedly deposited, each layer unit comprising an InGaN well layer, a GaN protective layer, and an AlGaN barrier layer sequentially deposited, the protective layer is formed as follows. The protective layer is grown at the same temperature as employed for the well layer. The growth rate of the protective layer is larger than 0.5 times and not larger than 1.1 times the growth rate of the well layer. The protective layer is formed so as to have a thickness of 5 Å to 8 Å at the start of growth of the barrier layer being formed thereafter.