The Ge (100) surface adsorbs Cs and O2in the same manner as does the Si (100) surface, but the resulting Ge/Cs/O surface does not exhibit negative electron affinity (NEA). Both Cs and O2are adsorbed in an ordered way—each adsorbate exhibiting the same 2 × 2 LEED pattern as the clean Ge substrate. Cs must be adsorbed before O2if the final Ge/Cs/O surface is to be ordered. The spectral photoemission data from the Ge/Cs (100) surface shows a threshold at 1.56 eV, while the threshold of the Ge/Cs/O surface is 1.12 eV, both of which are not band‐gap limited. From both the Ge/Cs and the Ge/Cs/O (100) surfaces, photoemission is characterized by hot electron emission over a positive energy barrier at the surface.