Abstract: A light-emitting device includes a semiconductor epitaxial structure that has a first surface and a second surface opposite to the first surface, and that includes a first semiconductor layer, an active layer, and a second semiconductor layer sequentially disposed in such order in a direction from the first surface to the second surface. The active layer includes well layers and barrier layers that are alternately stacked. The active layer has an upper surface that is adjacent to the second semiconductor layer, and a lower surface that is opposite to the upper surface. The first semiconductor layer is doped with an n-type dopant, which has a first concentration of 5E17/cm3 at a first point in the first semiconductor layer. The first point of the first semiconductor layer and the lower surface of the active layer have a first distance therebetween. The first distance ranges from 150 nm to 500 nm.