A light-emitting device comprises a first light-emitting semiconductor stack comprising a first active layer; a second light-emitting semiconductor stack below the first light-emitting semiconductor stack, wherein the second light-emitting semiconductor stack comprises a second active layer; a reflector between the first light-emitting semiconductor stack and the second light-emitting semiconductor stack; a protecting layer between the reflector and the second light-emitting semiconductor stack; and wherein the first light-emitting semiconductor stack further comprises a first semiconductor layer and a second semiconductor layer sandwiching the first active layer, the second light-emitting semiconductor stack further comprises a third semiconductor layer and a fourth semiconductor layer sandwiching the second active layer, wherein the second semiconductor layer has a first band gap, the third semiconductor layer has a second band gap, and the protecting layer has a third band gap between the first band gap and the second band gap.