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.