We investigate the influence of layer thicknesses and interface modifications on the fundamental electronic gap of Si/SiO2 multilayers by a combined ab initio calculation and photoluminescence (PL) analysis. For the band gap calculations different Si/SiO2 interface models are studied. Experimentally investigated multiple quantum wells are prepared by remote plasma-enhanced chemical vapor deposition and rapid thermal annealing. The well-width dependence of the band gap obtained from PL measurements is much weaker than found in previous studies. This sublinear variation is in accordance with simulated electronic band gaps for hydrogen-free Si/SiO2 interfaces. The presence of hydrogen at the interfaces enforces the confinement effect for the band gap. Materials involved: nanocrystalline silicon, amorphous silica, beta-cristobalite silica, and Si/SiO2 interface. (c) 2007 American Vacuum Society.