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 comprises: 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; and at least one third barrier layer between the second barrier layer and the first conductive type semiconductor layer, the plurality of well layers comprises: a first well layer between the first barrier layer and the second barrier layer, the first well layer having a third band gap; and a second well layer between the second barrier layer and the at least one third barrier layer, the second well layer having a second band gap, the first well layer has a thickness thinner than that of the second well layer; and the third band gap is different from the first band gap, wherein the first conductive type semiconductor layer comprises an n-type dopant, and the second conductive type semiconductor layer comprises a p-type dopant, wherein the third band gap is wider than the second band gap, wherein the first well layer of the plurality of well layers is nearest to the second conductive type semiconductor layer, wherein the first well layer has a thickness corresponding to a range from about 30% to about 60% of that of the second well layer, and wherein the first well layer has an indium content less than that of the second well layer and a compositional formula of In x Ga 1-x N (0,07<x<0,08), or has an indium content greater than about 45% of that of the second well layer. 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 comprises: 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; and at least one third barrier layer between the second barrier layer and the first conductive type semiconductor layer, the plurality of well layers comprises: a first well layer between the first barrier layer and the second barrier layer, the first well layer having a third band gap; and a second well layer between the second barrier layer and the at least one third barrier layer, the second well layer having a second band gap, the first well layer has a thickness thinner than that of the second well layer; and the third band gap is different from the first band gap, wherein the first conductive type semiconductor layer comprises an n-type dopant, and the second conductive type semiconductor layer comprises a p-type dopant, wherein the third band gap is wider than the second band gap, wherein the first well layer of the plurality of well layers is nearest to the second conductive type semiconductor layer, wherein the first well layer has a thickness corresponding to a range from about 30% to about 60% of that of the second well layer, and wherein the first well layer has an indium content less than that of the second well layer and a compositional formula of In x Ga 1-x N (0,07<x<0,08), or has an indium content greater than about 45% of that of the second well layer.