We have studied the scanning tunneling microscope-induced luminescence of GaN at low temperature. The emitted photons are investigated using bias spectroscopy techniques. Near band edge emission is detected at low temperature at tip biases exceeding V-t=3.25 V. Corresponding luminescence images reveal a correlation between threading dislocations and nonradiative recombination. A hole diffusion length of L-D= 30-55 nm is evaluated from the extent of the nonluminescent areas. Preliminary assessment of luminescence morphology is performed with standard cathodoluminescence.