This letter describes the effect of isochronal anneals on polycrystalline gallium arsenide solar cells, whose grain‐boundary edges have been passivated by selective anodization. Both the deterioration of this anodic oxide with temperature, as well as treatments for its full recovery and stabilization, are outlined in this Letter. This treatment consists of a rinse in strong HCl, and is carried out on cells after they are completely fabricated. It is proposed that conversion of the arsenic oxide component to its more stable hydroxide or chloride takes place during this treatment.