The surface electronic states of p- type GaN and its effect on the light- emitting diodes (LEDs) containing such p- GaN layers are studied. The surface band bending of p- GaN layers prepared from different growth conditions are determined by ultraviolet photoemission spectroscopy and X- ray photoemission spectroscopy. By either way, it is found that the surface band bending depends on the growth conditions and is reduced by increasing Mg concentration, growth temperature, and N-2(-) rich ambient. A further reduction in band bending is found with a postannealing at 750 degrees C in N-2, resulting in a similar reduction of the operation forward voltage of the LED containing such a p- GaN layer. The mechanism involved is discussed. (c) 2005 The Electrochemical Society.