A light emitting device is provided. The light emitting device comprises an active layer comprising a plurality of well layers and a plurality of barrier layers. The bather layers comprise a first barrier layer having a first band gap which is the nearest to the second conductive type semiconductor layer, a second barrier layer adjacent to the first barrier, and a third barrier layer between the second bather layer and the first conductive type semiconductor layer. The well layers comprise a first well layer having a third band gap different from the first band gap between the first and second bather layers, and a second well layer between the second barrier layer and the 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.