We present Auger-electron spectroscopy, low-energy electron diffraction, and Δ φ measurements of Cs adsorption on Si (100) and subsequent oxidation of the substrate. Our data provide evidence against complete charge transfer from the alkali metal to Si as proposed recently. The amount of Si O 2 produced by alkali-metal-promoted low-temperature oxidation of silicon is found to be strictly proportional to the alkali-metal coverage, which, together with measured changes in the work function during oxidation, allows us to question some of the current mechanisms put forward to explain this phenomenom.