The disclosed light emitting device includes an intermediate layer interposed between the light emitting semiconductor structure and the substrate. The light emitting semiconductor structure includes a first conductivity-type semiconductor layer, a second conductivity-type semiconductor layer, and an active layer interposed between the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer, wherein the active layer has a multi quantum well structure including at least one period of a pair structure of a quantum barrier layer including AlxGa(1-x)N (0