The photoluminescence band in porous Si is found to shift monotonically toward lower energy at a rate of −(18±5) meV/GPa if a hydrostatic pressure of up to 5 GPa is applied with liquid argon, in contrast to a convex behavior of the shift observed when a methanol–ethanol mixture is used as the pressure‐transmitting medium. The data show that the electronic energy gap relevant to the luminescence is intrinsically reduced by the hydrostatic compression but has a distinct solvatochromic character. ©1995 American Institute of Physics.