According to one embodiment, a semiconductor light emitting device includes first and second conductive layers, a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a light emitting part. The second semiconductor layer is provided between the first conductive layer and the first semiconductor layer. The light emitting part is provided between the first and second semiconductor layers. The second conductive layer is in contact with the second semiconductor layer and the first conductive layer between the second semiconductor layer and the first conductive layer. The first and second conductive layers are transmittable to light emitted from the light emitting part. The first conductive layer includes a polycrystal having a first average grain diameter. The second conductive layer includes a polycrystal having a second average grain diameter of 150 nanometers or less and smaller than the first average grain diameter.