Solar cells built on polycrystalline gallium arsenide usually have very leaky reverse characteristics and, consequently, low open-circuit voltage. These problems arise from the effect of the Schottky diode made on the grain boundary, which behaves like n+-material. This diode shunts the active Schottky solar cell and deteriorates its performance characteristics. In this letter we describe the use of selective-anodization techniques to provide an insulating barrier over the edge of the grain boundary in order to passivate it. Leakage current reduction of 5–6 decades has been achieved by this method, with both aqueous and nonaqueous anodization methods.