The present disclosure relates to a III-nitride semiconductor light-emitting device including a substrate with a first groove and a second groove formed therein, the substrate including a first surface and a second surface opposite to the first surface, a plurality of III-nitride semiconductor layers including a first semiconductor layer formed over the first surface of the substrate, a second semiconductor layer formed over the first III-nitride semiconductor layer, and an active layer disposed between the first and second III-nitride semiconductor layers and generating light by recombination of electrons and holes, a first opening formed on the first groove, a second opening formed on the second groove, a first electrode electrically connected from the second surface to the first III-nitride semiconductor layer through the first groove, and a second electrode electrically connected from the second surface to the second III-nitride semiconductor layer through the second groove and the second opening.