The effect of the wavelength upon the modification of the archetypical nonsubstituted alkanethiolate (AT) selfassembled monolayers (SAMs) on Au(111) by ultraviolet (UV) light was investigated. As a test system, the dodecanethiolate monolayer was selected, while the wavelength of the UV light was varied in two steps from 254 to 375 nm, which is a relevant range for a variety of inexpensive UV sources as well as custom-made and commercial lithography setups. The absolute cross sections of the most prominent and application-relevant UV-induced processes, above all photooxidation of the thiolate anchoring groups to sulfonates, were determined. They were found to decrease exponentially with increasing wavelength, with an effective "wavelength attenuation parameter" of ∼24 nm. This behavior was rationalized within a model assuming the primary role of UV-induced hot electrons, originating from the substrate and triggering an excitation and subsequent oxidation of the sulfur atoms by their reaction with oxygen molecules, penetrating to the SAM−substrate interface across the SAM matrix. The observed behavior and the absolute values of the photooxidation cross sections represent a useful "tool" for the estimation of a proper dose or dose range in the applications involving modification of AT SAMs and thiolate SAMs in general by UV light.