Magnesium oxide (MgO) thin films with sharp interfaces were deposited by sputtering of a Mg target on Si. The film stack was characterized using spectroscopic ellipsometry and transmission electron microscopy and the film static dielectric constant (kappa) and interface traps were determined. An amorphous SiO2 layer was found at the MgO/Si interface as a result of subcutaneous Si oxidation. kappa for the MgO films was found to be about twice that of SiO2, and the interface trap densities of MgO/Si were found to be comparable with SiO2/Si, rendering MgO competitive with all presently considered high-kappa dielectrics. (c) 2006 American Institute of Physics.