According to one embodiment, a semiconductor light emitting device includes n-type and p-type semiconductor layers, barrier layers, and a well layer. The n-type and p-type semiconductor layers and the barrier layers include nitride semiconductor. The barrier layers are provided between the n-type and p-type semiconductor layers. The well layer is provided between the barrier layers, has a smaller band gap energy than the barrier layers, and includes InGaN. At least one of the barrier layers includes first, second, and third layers. The second layer is provided closer to the p-type semiconductor layer than the first layer. The third layer is provided closer to the p-type semiconductor layer than the second layer. The second layer includes AlxGa1−xN (0