Silicon (Si) doped gallium nitride (GaN) layer's are grown on sapphire substrates with aluminium nitride (AlN) buffer layers by metalorganic chemical vapor deposition. As-grown GaN surfaces are roughened with hydrogen (H-2) plasma produced by supplying microwave power. The surface of GaN treated with H-2 plasma is observed with atomic force microscopy, and field emission characteristics are measured. The turn-on average electric field between the GaN and anode electrode is estimated to be as low as 12.4 V/mum. (C) 2003 American Vacuum Society.