A theory for carrier mobilities at weakly inverted Si surfaces is described. The theory treats transport of carriers across barriers in regions of statistically variable surface potentials. The potential variations are related to an earlier model proposed by Nicollian and Goetzberger to explain trapping phenomena. Measurements of surface conductance at inverted Si surfaces are presented which extend to lower free‐carrier populations than previously reported work. For bothpandnsurface channels, the measurements show a region of near constancy in mobility at very low surface densities followed by a rapidly increasing mobility at voltages near the conventional inversion threshold. The general features of these measurements and of their temperature variations correlate well with the theoretical model proposed.