A method of manufacturing a
semiconductor element of good characteristics at a reduced manufacturing cost is provided. The manufacturing method of the
semiconductor element includes a GaN-containing
semiconductor layer forming step, an
electrode layer forming step, a step of forming an Al film on the GaN-containing semiconductor layer, a step of forming a
mask layer made of a material of which
etching rate is smaller than that of a material of the Al film, a step of forming a
ridge portion using the
mask layer as a
mask, a step of retreating a position of a side wall of the Al film with respect to a position of a side wall of the
mask layer, a step of forming, on the side surface of the
ridge portion and the top surface of the
mask layer, a protective film made of a material of which
etching rate is smaller than that of the material forming the Al film, and a step of removing the Al film and thereby removing the
mask layer and a portion of the protective film formed on the top surface of the mask layer.