Deposition of gallium oxide and indium oxide on GaAs (001) was investigated by the alternating supply of triethylgallium (TEGa) or trimethylindium (TMIn), and hydrogen peroxide (H2O2). A pressure-control method was newly developed to produce precisely controlled surge pulses of source gases. Strong temperature dependence of the growth rate per source cycle obtained for the oxide deposition was caused by the decomposition of metalorganics, and by the thermal desorption of the oxide during the deposition. A critical thickness of 20 nm for the thermal desorption of gallium oxide was observed, which gives the upper limit of the promotive effect of underlying GaAs oh thermal desorption of gallium oxide. With implications for in situ process use, deposition of GaAs on gallium oxides and on indium oxides was performed by chemical beam epitaxy, and the differences between the two oxides were discussed from the viewpoint of gallium-atom-induced desorption and selectivity for GaAs deposition.