A light-emitting device includes a substrate, having a first surface and second surface opposite to the first surface; a light-emitting stack, formed on the first surface of the substrate, the light-emitting stack including a first semiconductor layer, an active layer and a second semiconductor layer, wherein the active layer is formed between the first conductive semiconductor layer and the second conductive semiconductor layer; and a distributed Bragg reflection structure (DBR), formed on the second surface of the substrate, including a plurality of dielectric-layer pair formed sequentially on the second surface, wherein each of the dielectric-layer pairs includes respectively a first dielectric layer having a first optical thickness and a second dielectric layer having a second optical thickness, and wherein from the second surface, the first dielectric layer of each of the dielectric-layer pairs is thicker than the first dielectric layer of the adjacent previous dielectric-layer pair.