The photoluminescence spectrum of undoped epitaxial wurtzite GaN layers on sapphire was measured for applied hydrostatic pressures up to 73 kbar at 9 K and up to 62 kbar at 300 K. The pressure dependences of theI2exciton recombination line and the ‘‘yellow’’ band (2.2 eV band at ambient pressure) were examined at 9 and 300 K, and the series of donor‐acceptor‐pair emission lines was analyzed at 9 K. From theI2lines, it was found that the band gap increases with pressure by 4.4±0.1 meV/kbar at 9 K and 4.7±0.1 meV/kbar at 300 K. ©1995 American Institute of Physics.