A group III nitride semiconductor light-emitting device includes: a conductive support; a p-electrode positioned on the support, a p-type layer containing a group III nitride semiconductor, an active layer and an n-type layer having a first surface, which are positioned in turn on the p-electrode; and an n-electrode positioned on the first surface of the n-type layer. A groove is formed in the first surface of the n-type layer in a pattern such that the first surface of the n-type layer is continuous. A light-transmitting insulating film is formed on side surface and bottom surface of the groove. The groove has a depth at least reaching the p-type layer. The n-electrode is formed in wiring form.