We report strong differences on the quantum-confined Stark effect (QCSE) behavior between Si/SiO2 quantum dots (QDs) and quantum wells (QWs). In QWs, the QCSE exhibits strong non-linearities, which can be fitted to second and/or fourth order polynomials with respect to the applied electric field (E-F) depending on the QW size and energy level. In contrast, for QDs the QCSE behavior is practically linear with the applied field. These differences are explained by means of the time-independent perturbation theory, where we show that for QWs, the parity differences between the (ID) wavefunctions and the perturbation potential make the first and third order corrections to vanish, while this parity difference is relaxed in QDs, making first order corrections (linear in E-F) to prevail with respect to the high-order contributions. (C) 2004 Elsevier B.V. All rights reserved.