Nanophase GaAs produced by organometallic synthesis was studied by Ga-71, Ga-69, and As-75 nuclear magnetic resonance (NMR) as well as x-ray diffraction. The structure of the samples synthesized below 250 degrees C is predominantly amorphous. Raising the temperature of synthesis (or post-synthesis annealing) above 280 degrees C improves significantly the crystallinity as evidenced by the appearance of a sharp bulklike Ga-71 (and Ga-69) peak. In addition, a sharp peak shifted up-field also appears. Other NMR features of this up-field shifted peak are very similar to the bulklike peak including quadrupole interactions and spin-lattice and spin-spin relaxations. These results are consistent with the presence of stacking faults in nanocrystalline GaAs.