The Cs/GaAs(110) system has been characterized using the techniques of angle‐resolved ultraviolet photoemission spectroscopy and medium energy ion scattering spectroscopy. In agreement with previous studies, the adsorption of Cs on the GaAs(110) surface at room temperature is found to cause a decrease in the work function by ∼3.6 eV. In contrast to analogous measurements on metal surfaces, no minimum is observed in the work function change (Δφ) vs Cs coverage (Θ) up to saturation. Using medium energy ion scattering, the absolute saturation coverage of Cs/GaAs(110) at room temperature has been determined to be (4.0±0.1)×1014atoms⋅cm−2which corresponds to the density of metallic Cs. Based upon photoemission measurements, the lack of Fermi‐level emission indicates that the interface is nonmetallic at this concentration. The implications of these results are discussed in comparison with alkali metal adsorption on metal surfaces.