A nitride semiconductor light emitting device comprises a first nitride semiconductor layer, an active layer of a single or multiple quantum well structure formed on the first nitride semiconductor layer and including an InGaN well layer and a multilayer barrier layer, and a second nitride semiconductor layer formed on the active layer. A fabrication method of a nitride semiconductor light emitting device comprises: forming a buffer layer on a substrate, forming a GaN layer on the buffer layer, forming a first electrode layer on the GaN layer, forming an InxGa1-xN layer on the first electrode layer, forming on the first InxGa1-xN layer an active layer including an InGaN well layer and a multilayer barrier layer for emitting light, forming a p-GaN layer on the active layer, and forming a second electrode layer on the p-GaN layer.