A red light emitting device, a method of fabricating a light emitting device, a light emitting device package, and a lighting system are provided. The red light emitting device may include a first semiconductor layer having a first conductivity, an active layer provided on the first semiconductor layer and including a quantum well and a quantum barrier, a second semiconductor layer having a second conductivity and provided on the active layer, a third semiconductor layer having the second conductivity on the second semiconductor layer, a fourth semiconductor layer having the second conductivity on the third semiconductor layer, and a fifth semiconductor layer having the second conductivity on the fourth semiconductor layer. The third semiconductor layer and the fourth semiconductor layer may include an AlGaInP-based semiconductor layer, and an Al composition of the fourth semiconductor layer may be lower than an Al composition of the third semiconductor layer.