A semiconductor element includes: a substrate having a first surface, a second surface, and at least one lateral surface; and a semiconductor layer formed on the second surface. The at least one lateral surface includes: at least one flat region, a first region that extends along a first direction parallel to the first surface at a position apart from the first surface and the second surface, wherein a surface roughness of the first region is larger than a surface roughness of the flat region, and a second region that extends along the first direction parallel to the first surface at a position between the first region and the first surface and apart from the first surface, wherein a surface roughness of the second region is larger than the surface roughness of the flat region. The substrate includes, in an interior of the substrate, a plurality of modified portions.