A noncontact method which measures a density of electric charge on the semiconductor surface without bias, and hence, with no electric field in the oxide is used to monitor the evolution of surface charge during an early stage of thermal oxidation of silicon, i.e., from bare surface to oxide about 3 nm thick. It is shown that before positive charge associated with trivalent silicon in the SiO2/Si interface region is established, a surface charge is controlled by a negative charge most likely associated with nonbridging oxygen. A transition between these two regimes takes place in the oxide thickness range of about 1.5-2.5 nm. For oxide above 3 nm thick the surface charge is fully developed and remains constant with an increase of oxide thickness. (C) 2003 The Electrochemical Society.