The surface of a degeneratep-type GaAs crystal, cleaved in ultrahigh vacuum to expose the (110) plane, has been examined as a function of cesium coverage using several methods. Electron stimulated desorption (ESD) of ions upon bombardment of the surface by 100-eV electrons is found to be extremely sensitive to trace quantities of adsorbed impurities. The work function-coverage relation forCs+deposited from a Cs zeolite ion gun was determined using a retarding potential method; the energy dependence of electron reflection in the range 0–10 eV was found to differ markedly between the clean and cesiated surfaces.