The electron cyclotron resonance plasma oxidation of silicon was investigated usinginsitustatic spectroscopic ellipsometry during process and dynamic real time ellipsometry at oxidation temperatures between 80 and 400 °C and at various applied bias’. Successful optical modeling of the ellipsometric data was accomplished using a two layer model, in which the top layer is a pure silicon dioxide film over an interface layer. The kinetics results are compatible with the Cabrera–Mott theory for the oxidation by charged species in the limit of low electric field. The effect of applied bias suggests that the oxidizing species is O−. The energy activation is 0.18 eV, substantially lower than the thermal oxidation value.