The appearance of positive interfacial charge at the Si‐SiO2interface in metal (Al) ‐SiO2‐silicon structures illuminated by vacuum ultraviolet (≳ 9 eV) light (Al‐negative) or subjected to electron‐avalanche injection (Al‐positive) has been found to depend on water exposure of the SiO2layer. This finding raises the possibility that these effects can be explained by the diffusion of water‐related species (especially H), rather than by the diffusion of excitons, as has been previously proposed. Although we cannot unambiguously decide whether the source of the vacuum ultraviolet effect is diffusion of excitons or water‐related species, it appears more likely that the water enhances thedetectionefficiency of the diffusing species as they reach the Si‐SiO2interface.