Combined ultrahigh vacuum electrochemistry studies show that the presence of a submonolayer of sulfur on copper results in an approximately twofold increase in the anodic dissolution current in a mildly alkaline borate buffer solution when compared to S-free copper. X-ray photoelectron spectroscopy measurements reveal that S remains adsorbed on copper and exhibits no change in oxidation state. This chemistry could form the basis for the development of an anisotropic etch for copper in the microelectronics industry.