Utilizing a new complex-band-structure technique, the electronic structure of model Si-Si 1−xGe x and MOS superlattices have been obtained over a wide range of layer thickness d (11 ≤ d ≤ 110 A). For d ≥ 44 A, it is found that these systems exhibit a direct fundamental band gap. Further calculations of band-edge effective masses and impurity scattering rates suggest the possibility of a band-structure-driven enhancement in electron mobility over bulk silicon.