We present a simple and novel method of resistlessly patterning GaAs substrates with an oxide mask. The GaAs surface native oxide is optically modified into a stable gallium oxide mask, which then allows InAs to be grown with excellent selectivity by chemical beam epitaxy. The conventional approach to pattern wafers for selective growth is to use photoresist to pattern the silicon nitride or oxide first deposited on the wafers. Photoresist residue can remain even after elaborate cleaning and the molecular scale features can impede selectivity during growth. This method is a one-step resistless process that eliminates such photoresist related problems. Our understanding of the patterning process and results on the selective growth of InAs are presented. ©1997 American Institute of Physics.