Disclosed in an embodiment is a semiconductor device comprising: a semiconductor structure comprising a first conductive type semiconductor layer, a second conductive type semiconductor layer, and an active layer disposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer; a second electrode electrically connected to the second conductive type semiconductor layer; and a reflective layer disposed under the second electrode, wherein the second conductive type semiconductor layer comprises a first sub-layer and a second sub-layer disposed between the first sub-layer and the active layer and having an aluminum (Al) composition higher than that of the first sub-layer, the reflective layer comes into contact with the lower surface of the second sub-layer, and the second electrode comes into contact with the first sub-layer.