According to one embodiment, a semiconductor light emitting device includes: a foundation layer, a first semiconductor layer, a light emitting part, and a second semiconductor layer. The foundation layer includes a nitride semiconductor. The foundation layer has a dislocation density not more than 5×108 cm−2. The first semiconductor layer of a first conductivity type is provided on the foundation layer and includes a nitride semiconductor. The light emitting part is provided on the first semiconductor layer. The light emitting part includes: a plurality of barrier layers; and a well layer provided between the barrier layers. The well layer has a bandgap energy smaller than a bandgap energy of the barrier layers and has a thickness larger than a thickness of the barrier layers. The second semiconductor layer of a second conductivity type different from the first conductivity type, is provided on the light emitting part and includes a nitride semiconductor.