This article describes the influence of the angle of incidence of the interaction of oxygen ions with GaAs surfaces and the effects these interactions have on compositional quantification by secondary ion mass spectrometry. Both Auger electron and small spot size x-ray photoelectron spectroscopies were used to study the chemistry of the bombarded surfaces. The oxidation states of gallium and arsenic and the overall gallium-to-arsenic ratios were found to vary in a systematic way with angle of incidence. Changes in gallium and arsenic surface chemistry are correlated with secondary ion yields of dopants or impurity atoms.