We describe a photolithographic method for the direct modification and micropatterning of the surface chemical structure of self-assembled monolayers. End-functional azobenzene alkanethiols are designed and synthesized so that, when self-assembled onto gold substrates, an acid-sensitive tert-butyl ester end group is positioned at the air−monolayer interface. Upon exposure to UV radiation in the presence of a photoacid generator, the tert-butyl ester groups are removed in the form of butylene gas to form surface carboxylic acid groups. The orientation of the monolayers and photochemical surface modification reactions are characterized by X-ray photoelectron spectroscopy measurements. The photochemical change from hydrophobic tert-butyl ester groups to hydrophilic carboxylic acid groups causes a significant change in wettability reflected in a water contact angle change from 89 to 28°, respectively. Surface chemical modifications may be patterned on a microscale by simply irradiating the self-assembled mono...