The Si 2p and O 1s core-level photoemission peaks and the valence band peaks for silicon oxide films grown on crystalline silicon have been observed to shift to higher binding energy as a function of increasing film thickness. The physical basis for this shift has been ascribed to a variety of mechanisms including initial state effects, final state effects, and extrinsic effects. By constructing a structurally homogeneous silicon oxide film consisting of H10Si10O15 on silicon, initial state effects have been minimized and the magnitude of final state effects directly measured. Unlike previous studies utilizing the H8Si8O12 cluster, the cluster precursor utilized in these studies is large enough to allow direct observation of the theoretically predicted asymptotic behavior in the core-level shift as a function of cluster layer thickness prior to the onset of film charging.