The effect of hydrostatic strain on wurtzite GaN is studied theoretically using an sp 3 d 5 -sp 3 empirical tight-binding model (ETBM). The model incorporates all nearest-neighbor and some second-nearest neighbor interactions within the two-center approximation. The second-nearest neighbor interactions excluded are the cation-cation interactions involving the Ga 3d orbital. Strain is included by scaling the two-center integrals appropriately. The strain is, therefore, modeled without invoking deformation potential theory, eliminating the need for additional strain parameters. The effective band gap has been calculated for various hydrostatic strains and the results compared with published experimental data. The theory reproduces the sublinear dependence of the band gap with pressure, and the calculated pressure dependence of the band gap and the hydrostatic deformation potential are found to agree well with experiment and with previously published results calculated via ab initio techniques, showing the validity of the present approach.