A model based on space‐charge assisted diffusion of O−is proposed to describe the rapid thermal oxidation kinetics of silicon in dry oxygen ambient. The space‐charge region within the growing oxide layer is assumed to have a constant planar charge density which results in a characteristics length, &lgr;c, the extend of the space‐charge region. The diffusion of O−and therefore the oxide growth rate will be driven by two components, the concentration gradient and space‐charge drift. The discrepancy in the calculated values of diffusion activation energies for O−is explained by comparing the strength of the space‐charge regions. The strength of space charge depends on the range of photon energies irradiated by the heating lamps used in different rapid thermal processors. ©1995 American Institute of Physics.