Quantum confinement effects in two-dimensional(2D) Si and zero-dimensional (OD) Si structures, fabricated from silicon-on-insulator wafers, have been comparatively studied primarily by X-ray photoelectron spectroscopy (XPS), focusing on the energy shifts of the valence band maximum (VBM). As a result, it was found that the VBM obviously shifts toward higher binding energies during layer thinning of Si well and size reduction of Si dots, in accordance with quantum mechanical consideration.