a-Si ∶H/SiO2 multiple quantum wells (QWs) are fabricated by plasma enhanced chemical vapor deposition (PECVD) and subsequent different thermal annealing. Among them the annealed sample under 1100 ℃ in vacuum can be transferred into nc-Si:H/SiO2 QWs, and the size of formed nc-Si:H is controllable and it matches the thickness of a-Si ∶H sublayer. The optical absorptivity of a-Si ∶H/SiO2 QWs is compared with that of a-Si ∶H under the same fabrication condition, the former is higher evidently in the UV/Visible spectrum with the absorption edge blue-shifted, which shows that a-Si ∶H/SiO2 QWs has an obvious quantum confinement effect. So it is feasible to use a-Si ∶H/SiO2 QWs to enhance the efficiency of silicon solar cells. In addition, the formation of nc-Si:H/SiO2 QWs with controllable size built the basis for new-type nanocrystalline silicon solar cells.