The dielectric functions ofa‐Si prepared by Si ion implantation in Si and of subsequently thermally annealeda‐Si have been measured by means of spectroscopic ellipsometry. Differences are observed that may be accounted for only partially by differences in density, recrystallization during preparation of the anneal‐stabilizeda‐Si state, or differences in the surface condition of the samples. Intrinsic changes in the bond polarizability are thus indicated. Comparison of the x‐ray photoemission results for the Si 2pcore levels and the valence band states of the as‐implanted and anneal‐stabilizeda‐Si samples reveals measurable changes in the valence charge distribution sufficient to substantiate a change in the bond polarizability.