The effect of annealing of the n-GaAs semiconductor on its characteristics in photoelectrochemical (PEC) systems has been investigated. The photocurrent densities vs. potential plots were improved by annealing. Cell efficiency and short-circuit current densities were enhanced for the annealed n-GaAs. The effect of the rate of cooling of heated n-GaAs wafers was also investigated. It was found that the slowly cooled electrodes gave better dark current density vs. potential plots, for samples annealed below 600 C. For samples annealed at higher temperatures, quenching gave better dark-current density vs. potential plots. For n-GaAs, slowly cooled electrodes from temperatures below 600 C showed better photocurrent density vs. potential plots and higher efficiency. n-GaAs samples, quenched from temperatures above 700 C, showed better photocurrent density vs. potential plots and higher efficiency than their slowly cooled counterparts.