We report a structural and electrical study of sputter-deposited SiO 2 /MgO barriers for developing magnetic Si-based transistors. We propose that SiO2 /MgO tunneling barriers may utilize spin-filtering by achieving crystalline MgO (001) while reducing spin-scattering due to the Si/ SiO2 interface. We find that MgO (<3 nm thick) crystallizes with (001) preferred orientation on thermally oxidized Si (<2 nm). Typical processing temperatures do not cause significant intermixing with SiO 2 or ferromagnetic electrode. Conversely, MgO on Si is amorphous up to 2 nm thick. Capacitance-voltage characteristics of MgO capacitors are influenced significantly by the density of interface-states, as high as 5× 1013 cm-2 eV-1 while Si/ SiO2 /MgO structures are electrically beneficial by reducing to 6× 1012 cm-2 eV -1.