We present a method for the controlled fabrication of stable nanostructures under ambient conditions. The surfaces under consideration, WSe2, are imaged by an atomic force microscope. By applying a voltage between the tip and the sample, we can control an etching process at the surface: different voltage thresholds for the creation and the growth of structures of one monolayer (Se–W–Se) depth are observed. Our measurements on p‐doped WSe2 strongly support an electrochemical corrosion reaction in a physisorbed water film. This method allows the in situ preparation and characterization of individual nanometer‐sized structures on WSe2 and other metal dichalcogenides. © 1996 American Institute of Physics.