A semiconductor light emitting device includes a light-transmissive substrate, a light-transmissive buffer layer disposed on the light-transmissive substrate, and a light emitting structure. The light-transmissive buffer layer includes a first layer and a second layer having different refractive indices and disposed alternately at least once. The light emitting structure includes a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer sequentially disposed on the buffer layer.