Onto a surface of an Al.sub.xGa.sub.yIn.sub.1-x-yAs.sub.zP.sub.1-z (0.ltoreq.x, y, z.ltoreq.1) layer including GaAs alone or an InP substrate, an electron beam controlled to an arbitrary electron beam diameter and current density is irradiated so as to selectively substitute or generate Ga.sub.2O.sub.3 for a natural oxide layer formed on the Al.sub.xGa.sub.yIn.sub.1-x-yAs.sub.zP.sub.1-z, layer surface, then the Al.sub.xGa.sub.yIn.sub.1-x-yAs.sub.zP.sub.1-z layer surface is dry-etched by a bromide in single atomic layer units, whereby the natural oxide layer other than the part substituted by the Ga.sub.2O.sub.3 and Al.sub.xGa.sub.yIn.sub.1-x-yAs.sub.zP.sub.1-z substrate are removed.