Diodes with transparent top contacts were fabricated by depositing indium oxide layers onto n-type GaAs by means of reactive evaporation of In in the presence of oxygen. The electrical characteristics as well as the structural properties and chemical composition of the resulting junctions were studied using Auger electron spectroscopy, x-ray diffraction, optical absorption, capacitance-voltage, and dark current-voltage measurements. The best diodes were obtained under deposition conditions of substrate temperature 250°C and oxygen pressure 5×10-4 mbar; these diodes exhibited a Schottky barrier height of 0.85 V with an ideality factor of 1.04. The indium oxide films were found to be polycrystalline and to have an electrical resistivity of 3×10-4 Ω cm and an optical transmittance above 90% over the whole visible range. The effect of deviations from the optimal deposition parameters on the diode properties is discussed.