A light-emitting device comprises a substrate, at least one light-emitting structure configured to emit light beams and positioned on the substrate, and a ring-shaped photonic crystal structure positioned in the light-emitting structure. The ring-shaped photonic crystal structure includes a plurality of pillars positioned in the light-emitting structure and a plurality of ring-shaped openings surrounding the pillars. The distance between the ring-shaped openings is preferably between 0.2λ and 10λ, and λ represents the wavelength of the light beam.