[en] We use scanning tunneling microscopy (STM) in ultrahigh vacuum (UHV) to probe the local atomic structure and the electronic properties of the phase change alloy Ge 2 Sb 2 Te 5 (0001) grown on Si (111) by molecular beam epitaxy. In order to obtain a clean surface, the mixed native oxides on the GST surface were removed by dipping the sample in de-ionized water followed by annealing at 200 C in UHV. We realized images with atomic resolution in constant-current mode at different voltages in order to distinguish different chemical elements on the surface. Local variations in the atomic corrugation and lattice constants are found and analyzed in detail. Using the spectroscopy mode, we find a band gap of about 500 meV. A p-type doping becomes apparent in agreement with photoelectron spectroscopy data.