Disclosed is a light-emitting device. The light-emitting device comprises: a first conductivity type semiconductor layer; a second conductivity type semiconductor layer; and an active region comprising a material having a composition of AlxInyGa(1-x-y)N (0≦x≦1, 0≦y≦1, 0≦x+y≦1) between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer, wherein the active region comprising: a plurality of barriers and one well disposed between any two of adjacent barriers, wherein the barriers comprises a composite barrier and a single barrier while the composite barrier is composed of a gradient layer having an element with a gradient concentration therein and a first non-gradient layer having a non-gradient composition, and the single barrier is composed of a second non-gradient layer adjacent to the first conductivity type semiconductor layer or the second conductivity type semiconductor layer.