The reaction of cubic gallium arsenide (GaAs) with ammonia yielded gallium nitride (GaN). Powder X-ray diffraction patterns of the GaN products showed that they are a mixture of c- and w-GaN, while their Ga MAS NMR spectra revealed that they have the other phase of GaN besides c- and w-GaN and the high reaction temperature (>= 900 degrees C) induces nitrogen deficiency in GaN. The peaks at 353 and 347 ppm in the Ga-71 MAS NMR spectra were tentatively assigned to c-GaN and an intermediate of w- and c-GaN in the stacking order, respectively. The observed Ga-71 chemical shifts of GaN, GaP, GaAs and GaSb in cubic phase were well correlated with the reciprocal of their band gaps. (c) 2005 Elsevier B.V. All rights reserved.