The optoelectronic properties of GaN with zinc-blende structure under hydrostatic pressure up to 120kbar are investigated employing the empirical pseudopotential method. The pressure coefficients of several critical-point band gaps are calculated and found to be in good agreement with the available experimental data. The refractive index decreases linearly with increasing pressure showing a negative pressure coefficient. At zero pressure, the agreement between our calculated optical dielectric constant and the existing experimental data depends on the model used for calculating the refractive index. (C) 2002 Elsevier Science B.V. All rights reserved.