The present invention relates to an III-nitride semiconductor light emitting device in which a single layer or plural layers made of Si.sub.xC.sub.yN.sub.z(x.gtoreq.0, y.gtoreq.0, x+y>0, z>0) are inserted into or under an active layer and it is directed to a technology in which Al(x)Ga(y)In(1-x-y)N(0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.x+y.ltoreq.1) of the hexagonal structure and Si.sub.xC.sub.yN.sub.z(x.gtoreq.0, y.gtoreq.0, x+y>0, z>0) of the hexagonal structure are combined together in view of the properties of the Si.sub.xC.sub.yN.sub.z(x.gtoreq.0, y.gtoreq.0, x+y>0, z>0) material.