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The Stark shift of the electronic energy levels in semiconducting rectangular quantum boxes with different sizes is investigated by the use of variational solutions to the effective-mass approximation for electric fields of various orientations with respect to the center axis of the box. The asymptotic expansions of the Stark shift are given in the limits of low and high fields, respectively; they clearly indicate that the Stark shift is a quadratic function of the electric field for low electric fields and is an approximate linear function of the electric field for high electric fields. Likewise, our results also show that the largest Stark shift is obtained for the field directed along the diagonal in a cubic box, and is found for the low field directed along a side of the box and for the high field along the diagonal in a rectangular one. The large Stark shift of the electron and hole trapped in a quantum box leads to an obvious reduction of the interband recombination. (C) 2008 Elsevier Ltd. All rights reserved.