A light-emitting device is capable of emitting a light having a wavelength ranging from 300 to 550 nm, and includes: a substrate; a p-type semiconductor layer disposed on the substrate; an active layer disposed on the p-type semiconductor layer; a n-type semiconductor layer disposed on the active layer and having a waveguide-disposing surface; and a waveguide structure formed on the waveguide-disposing surface of the n-type semiconductor layer and having a plurality of spaced apart nanorods extending from the waveguide-disposing surface.