A study was conducted of the effect of fluoride ions on the properties of an Si-SiO//2 structure in which the SiO//2 layer is doped with fluoride ions from electrolyte. It was found that fluoride ions have a significant effect on the properties of thermally oxidized Si and this includes the formation of a negative charge in the volume of the oxide. By changing the polarization conditions of the Si-SiO//2 structure in an electrolyte containing fluoride ions, it is possible to control the magnitude and spatial distribution of this charge.