The first subband energy at the valence band of self-assembled silicon quantum dots grown by low-pressure chemical vapor deposition on ultrathinSiO2/Sisubstrates has been measured as an energy shift at the top of the valence band density of states by using high-resolution x-ray photoelectron spectroscopy. The systematic shift of the valence band maximum towards higher binding energy with decreasing the dot size is shown to be consistent with theoretical prediction. The charging effects of the silicon dots and theSiO2layer by photoelectron emission during the measurements have been taken into account in determining the valence-band-edge energy. ©1998 American Institute of Physics.