Photon-stimulated ion desorption (PSD) from chlorine-adsorbed GaAs(100) and GaAs(111)B surfaces is investigated by using synchrotron radiation. Ga⁺ desorption was observed only from the Cl-adsorbed GaAs(100) surface while Cl⁺ desorption was observed from the both surfaces. These results are explained from the viewpoints of the difference in bonding state of chlorine atom at two types of GaAs surfaces. The photon energy dependence of Cl⁺ desorption yield suggests that the photo-ionization of Cl core levels is much more effective for the ion desorption than that of As core levels.