Experimental results are presented and analyzed in order to demonstrate the importance of scattering by charge centers at or near the Si/SiO2interface in the determination of the transport properties of inversion layer carriers in MOS structures. The measured mobility behavior clearly shows the relative importance of the effects of charges as a function of temperature and applied bias. The observations are compared with the existing theory of Coulomb scattering, and an attempt is made to present a theory which more correctly predicts the experimentally determined behavior.