The nature of the surface‐state charge (Qss) associated with thermally oxidized silicon has been studied experimentally using MOS structures. The effects of oxidation conditions, silicon orientation, annealing treatments, oxide thickness, and electric field were examined, as well as the physical location of the surface‐state charge. The results indicate that the surface‐state charge can be reproducibly controlled over a range , and that it is an intrinsic property of the silicon dioxide‐silicon system. It appears to be due to an excess silicon species introduced into the oxide layer near the silicon during the oxidation process.