A light emitting device comprising: a first conductive type semiconductor layer; a second conductive type semiconductor layer on the first conductive type semiconductor layer; and an active layer between the first conductive type semiconductor layer and the second conductive type semiconductor layer, the active layer comprising a plurality of well layers and a plurality of barrier layers, wherein the plurality of barrier layers comprise: a first barrier layer which is the nearest to the second conductive type semiconductor layer, the first barrier layer having a first band gap; a second barrier layer adjacent to the first barrier layer, the second barrier layer having a third band gap; and at least one third barrier layer having the first band gap between the second barrier layer and the first conductive type semiconductor layer, the plurality of well layers comprise: a first well layer between the first barrier layer and the second barrier layer, the first well layer having a second band gap; and a second well layer between the second barrier layer and the at least one third barrier layer, the second barrier layer is disposed between the first well layer and the second well layer, the third band gap is narrower than the first band gap and wider than the second band gap, wherein the second barrier layer is formed in a single layer of an InGaN-based semiconductor layer which has an Indium content greater than that of the first barrier layer and less than that of the first well layer or an AlGaN-based semiconductor layer which has an aluminum content less than that of the first barrier layer, wherein the second barrier layer is contacted with the first well layer and the second well layer, wherein the second barrier layer has the barrier height less than the barrier height of each of the first and third barrier layers. a first conductive type semiconductor layer; a second conductive type semiconductor layer on the first conductive type semiconductor layer; and an active layer between the first conductive type semiconductor layer and the second conductive type semiconductor layer, the active layer comprising a plurality of well layers and a plurality of barrier layers, wherein the plurality of barrier layers comprise: a first barrier layer which is the nearest to the second conductive type semiconductor layer, the first barrier layer having a first band gap; a second barrier layer adjacent to the first barrier layer, the second barrier layer having a third band gap; and at least one third barrier layer having the first band gap between the second barrier layer and the first conductive type semiconductor layer, the plurality of well layers comprise: a first well layer between the first barrier layer and the second barrier layer, the first well layer having a second band gap; and a second well layer between the second barrier layer and the at least one third barrier layer, the second barrier layer is disposed between the first well layer and the second well layer, the third band gap is narrower than the first band gap and wider than the second band gap, wherein the second barrier layer is formed in a single layer of an InGaN-based semiconductor layer which has an Indium content greater than that of the first barrier layer and less than that of the first well layer or an AlGaN-based semiconductor layer which has an aluminum content less than that of the first barrier layer, wherein the second barrier layer is contacted with the first well layer and the second well layer, wherein the second barrier layer has the barrier height less than the barrier height of each of the first and third barrier layers.