Electric charge in the GaAs native oxide formed by anodic oxidation and by plasma oxidation was successfully characterized utilizing contact potential difference measurements. Negative electric charge as high as 1012q/cm2was found in all oxide layers independent of their thickness. At room temperature this charge can be effectively screened out by absorption of polar molecules (organic solvents) which thermally desorb at 70 °C. Higher temperature annealing (70–180 °C) irreversibly reduces the charge in oxide by over an order of magnitude. It is shown that the oxide charge reflects the internal electric polarization created during the oxidation process.