Atomic-scale dynamics in thermal oxidation on Si(001) has been investigated by employing the reflectance difference (RD) oscillation technique. After reviewing the RD spectra reported for oxidized single-domain Si(001) surfaces, we report the results of dynamic measurements, which were carried out using a GaN semiconductor laser as the light source. RD traces show distinctly different behaviors depending on whether oxidation is in the passive (oxide growth) or active (etching) mode. The critical temperature-pressure conditions for onset of oxide growth have been identified. When oxide growth is continued to the second and subsequent layers, the RD amplitude shows oscillation from which we have extracted layer-specific kinetic parameters for the oxidation process. (C) 2003 Elsevier B.V. All rights reserved.