The authors developed modulation scanning tunneling microscope cathodoluminescence (STM-CL) spectroscopy where low-energy (similar to 100 eV) electrons field-emitted from scanning tunneling microscope(STM) tips were used as a bright excitation source. The modulation STM-CL spectroscopy of Si-doped GaAs (110) cleaved surfaces showed that the peak redshifted from GaAs band-edge luminescence in some of the sample positions. These position-dependent redshifts, which were explained by the transition related to local Si acceptors, demonstrated a spatial resolution of less than 600 nm in the modulation STM-CL spectroscopy. (c) 2008 American Vacuum Society.