Flat-topped mesas are formed on glassy carbon surfaces as a result of electrochemical oxidative treatment in aqueous sodium hydroxide. The topography of the anodically exposed glassy carbon was followed by phase detection interferometric microscopy. The appearance and the distribution of the mesas were found to be related to the mode of electrochemical treatment. A threshold time, a function of applied voltage, and a threshold voltage for the formation of the mesas were found. In addition, the physical size and number of the structures increased with applied voltage.