Junctions of transparent conducting oxides on III-V semiconductors have been prepared by deposition of indium oxide layers onto p-type InP and n-type GaAs by means of reactive evaporation of In in the presence of oxygen at different substrate temperatures. The electrical properties and chemical composition of these junctions have been investigated using current-voltage measurements in the dark at room temperature, capacitance-voltage measurements, and depth profiling by Auger electron spectroscopy. The best diodes were obtained by deposition at a substrate temperature near 250°C and oxygen pressure of 5×10-4 Torr. These diodes exhibit a Schottky barrier height of 0.80 eV for n-type GaAs and 0.87 eV for p-type InP with an ideality factor of 1.04. The Schottky barrier height decreases with decreasing deposition temperature for both substrates. The roles of the tunneling-transparent interface layer and interface region are theoretically considered. It is shown that as the deposition temperature is increased, the barrier height increases due to the accompanying reduction in the density of surface states, which are induced by elemental In at the interface.