According to one embodiment, in a semiconductor light emitting device, a substrate includes a first surface, a second surface opposite to the first surface, lateral surfaces intersected with the first surface and the second surface, first regions each provided on the lateral surface, and second regions each provided on the lateral surface. Each of the first regions has a first width and a first roughness. Each of the second regions has a second width smaller than the first width and a second roughness smaller than the first roughness. The first regions and the second regions are alternately arranged. A proportion of the sum of the first widths to a distance between the first surface and the second surface is 0.5 or more. A semiconductor laminated body is provided above the first surface of the substrate, and includes a first semiconductor layer, an active layer and a second semiconductor layer.