We have measured the hydrostatic pressure dependence of the photoluminescence (PL) of Si nanocrystals in SiO2 layers at room temperature and at pressures up to 50 kbar. The samples were fabricated by ion implantation and subsequent annealing. For the two samples measured, negative pressure coefficients of −0.4 and −0.6 meV/kbar were obtained. These values are not in good quantitative agreement with an estimate based on the quantum confinement model. Possible implications of this disagreement are discussed.