We report the results of a comparison study of photoluminescence (PL) from an In0.15Ga0.85N/GaN multiple-quantum-well (MQW) sample and an In0.11Ga0.89N thick epitaxial-layer sample, which have very similar band-gap energies. Large hydrostatic pressures were used for our investigations. The PL emissions in both samples were found to shift linearly to higher energy with applied pressure. In the MQW sample, the pressure response of the InGaN is dominated by the GaN layers, which leads to a significantly weaker pressure dependence as compared to the epilayer sample. Our results yield a pressure coefficient of 2.8×10-3 eV/kbar for the In0.15Ga0.85N/GaN MQW sample and 4.0×10-3 eV/kbar for the In0.11Ga0.89N epilayer. An abrupt decrease of PL intensity in both samples was observed at pressures above 100 kbar, indicating the carriers involved in the radiative recombination processes in the samples originate primarily from the adjacent GaN layers. © 1998 American Institute of Physics.