We have investigated the effect of hydrostatic pressure on interdiffusion in multilayers composed of alternating layers of amorphous Si (2.7 nm) and Ge (3.1 nm). Samples were annealed at 420 °C at pressures between 0 and 2.8 GPa in an externally heated diamond anvil cell. Interdiffusion was measured by monitoring the decay with annealing time of the intensity of the first‐order x‐ray reflection resulting from the effects of composition modulation. The decay curves for all pressures could be made to coincide by scaling the annealing times. This made it possible to separate the effects of pressure on the interdiffusivity from those of composition and structural relaxation. The interdiffusivity increased with applied pressure, with an activation volume of −5.0 cm3/mole, or −0.42 times the atomic volume of crystalline Si. ©1996 American Institute of Physics.