The band structure of strained Si (4–10 ML) on (001) GaAs, band lineups of the strained Si/(001)GaAs heterojunction, and confined energy levels of theSi3N4/Si/GaAsquantum well have been calculated via a pseudopotential method. It has been found that in this technically importantSi3N4/Si/(001)GaAsstructure, strained Si has a very narrow band gap (0.34 eV) at the&Dgr;⊥point in the Brillouin zone. For the strained Si/(001)GaAs heterojunction, the conduction band offsets from the&Dgr;⊥for Si to the &Ggr; valley for GaAs is 0.83 eV, and that from the&Dgr;⊥valley for Si to theXvalley for GaAs is 1.21 eV. The valence band offset is 0.25 eV. The lowest confined energy level in the conduction band of theSi3N4/Si/GaAsquantum well ranging from 4 to 10 monolayers is found to be 0.22–0.28 eV above the conduction band edge of strained Si, or 0.57–0.61 eV below the conduction band edge of GaAs, while the first confined energy level in the valence band is barely above the valence band maximum of GaAs. The accumulation and inversion take place at these confined energy levels. ©1997 American Institute of Physics.