A semiconducting GaN thin film with the 001 plane parallel to the surface grown by organometallic vapor phase epitaxy method on (110) sapphire was studied using x-ray diffraction. The line profiles of the GaN thin film along the [001] direction can be quantitatively reproduced assuming a strained lattice at the interface. The deformation and growth faults were determined to be equal and each is 0.2&percent;. Least-squares refinement on 42 independent peaks, after correcting for the first-order thermal diffuse scattering, gives the values of the Debye–Waller factor for Ga(B11=0.28,B33=0.26)and N(B11=0.38,B33=0.26)atoms. The wurtzite positional parameterufor this GaN thin film was found to be 0.3730, 1&percent; smaller than that in a strain-free single crystal(u=0.377),most probably resulting from the strain effects. ©1997 American Institute of Physics.