An increase in the photoinduced refractive-index change DELTAn in silica-based optical waveguides on silicon is described. The increase is attained by the consolidation of a core film in a reducing atmosphere. A maximum DELTAn of 3-9 x 10(-4) is obtained for the TE mode by UV laser irradiation at 248 nm. This is four times larger than that in conventional waveguides.