The Shubnikov-de Haas effect has been measured in silicon inversion layers as a function of temperature, carrier density, and oxide charge density. The dependence on oxide charge density provides a critical test of the theory of ionic scattering in the Shubnikov-de Haas effect. The data are found to be in excellent agreement with theory. The temperature dependence permits the study of electron effectie masses. We give a more detailed account of the dependence of the electron effective mass on ionic scattering and the effective mass extrapolated to zero ionic scattering. © 1978 The American Physical Society.