A GaN based III-V nitride semiconductor light-emitting device and a method for fabricating the same are provided. In the GaN based III-V nitride semiconductor light-emitting device including first and second electrodes arranged facing opposite directions or the same direction with a high-resistant substrate therebetween and material layers for light emission or lasing, the second electrode directly contacts a region of the outmost material layer exposed through an etched region of the high-resistant substrate. A thermal conductive layer may be formed on the bottom of the high-resistant substrate to cover the exposed region of the outmost material layer.