MOS‐capacitance measurements combined with neutron activation analysis show that positive charge at oxidized silicon surfaces can be increased by the presence of sodium in the oxidation system. The amount of charge depends then on the surface orientation and the oxide thickness. It can be decreased by low‐temperature heat treatment in water vapor or hydrogen. The same treatment can cause an effective reduction of the number of interface states. In both cases an explanation can be found in the formation of Si&sngbnd;H bonds.