We have studied the growth of gallium nitride (GaN) on (0001) sapphire substrates in a commercial (CVD Equipment Corp.) metalorganic chemical vapor deposition reactor. High quality epitaxial GaN films were obtained by deposition at 1000 degrees C from trimethylgallium and ammonia precursors (1.5 slpm total flow rate with V/III molar flow ratio of 5800) on a 24-nm-thick GaN buffer layer grown at 500 degrees C. X-ray rocking-curve measurements of films grown under these conditions showed a full width at half maximum of 0.28 degrees. The x-ray lattice parameter method was used to determine the residual stress in GaN films by measuring the c-axis and a-axis strains separately. The results indicate that residual stress in GaN him grown on sapphire is compressive and;is reduced as the buffer layer thickness increases.