A method of manufacturing a semiconductor element includes a first irradiation step in which a laser beam is irradiated to form, in the interior of the substrate, a plurality of first modified portions aligned along a first direction; a second irradiation step in which a laser beam is irradiated to form a plurality of second modified portions aligned along the first direction at a position adjacent to the plurality of first modified portions in the second direction; and a third irradiation step which a laser beam is irradiated to form a plurality of third modified portions aligned along the first direction at a position closer to the first surface than the first modified portions and overlapping the plurality of first modified portions in a thickness direction of the substrate.