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The large changes in the electronic structure in dilute III-V nitrides and other semiconductor alloys containing isoelectronic impurities of high electronegativity or low ionization energy can be explained by the band anticrossing model. Interaction between the localized levels introduced by a highly electronegative impurity, such as N in GaNxAs1−x, and the delocalized states of the host semiconductor causes a restructuring of the conduction band into E+ and E− subbands, which in this case effectively lowers the conduction band edge of the alloy. This restructuring is not only responsible for the reduction of the fundamental band gap energy but also accounts for the direct band gap nature in GaNxP1−x and the enhanced electron effective mass observed in GaNxAs1−x. Conversely, the incorporation of large-sized isoelectronic impurities with low ionization energy into III-V and II-VI compounds is found to induce a restructuring of the host valence band by the same anticrossing mechanism. Integration of the conduction and valence band anticrossing models provides an accurate description of the electronic structure of these alloys across their entire composition range. [ABSTRACT FROM AUTHOR]