Abstract: Onto a surface of an AlxGayIn1-x-yAszP1-z (0?x, y, z?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 Ga2O3 for a natural oxide layer formed on the AlxGayIn1-x-yAszP1-z, layer surface, then the AlxGayIn1-x-yAszP1-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 Ga2O3 and AlxGayIn1-x-yAszP1-z substrate are removed.