One embodiment of the present invention provides a gallium nitride (GaN)-based semiconductor light-emitting device (LED) which includes an n-type GaN-based semiconductor layer (n-type layer); an active layer; and a p-type GaN-based semiconductor layer (p-type layer). The n-type layer is epitaxially grown by using ammonia gas (NH3) as the nitrogen source prior to growing the active layer and the p-type layer. The flow rate ratio between group V and group III elements is gradually reduced from an initial value to a final value. The GaN-based LED exhibits a reverse breakdown voltage equal to or greater than 60 volts.