Measurements of the standard deviation &sgr;sof the surface potential fluctuations in MOS structures were performed by the conductance technique of Nicollian and Goetzberger for different temperatures and surface potentials. The values of &sgr;swere compared with the three‐dimensional mathematical model suggested by Brews and the quasiuniform model of the surface potential fluctuations generated by interface charge inhomogeneities. Good agreement was obtained with the model of Brews. We conclude that the interface charges are not agglomerated in the form of charge islands but are more or less evenly distributed. For the lower limit of the minimum wavelength of the interface charge inhomogeneities, we obtain a value of 75 A˚. The upper limit of 100 A˚ as assumed by Brews seems to be reasonable. Negative interface charges are either absent or at most present at a low level.