This paper reviewed the recent study on the growth kinetics of very thin oxide layers on the Si(001) surface performed by a real-time monitoring method of Auger electron spectroscopy combined with reflection high energy electron diffraction (RHEED-AES). The RHEED-AES method enabled us to measure simultaneously the oxide coverage and etching rate during Si thermal oxidation. The time evolution of O KLL Auger electron intensity is applicable for discriminating definitely three kinds of oxidation schemes appearing at the initial stage: Langmuir-type adsorption, two-dimensional (2D) oxide island growth and active oxidation. In the Langmuir-type adsorption, the time evolution of RHEED intensity ratio between the half-order spots of (1/2, 0) and (0, 1/2) I_{(1/2, 0)}/I_{(0, 1/2)} suggested emission of Si atoms from the oxidized area, which was interpreted in terms of the interfacial strain due to volume expansion resulting from oxidation. In the 2D oxide island growth and active oxidation, the I_{(1/2, 0)}/I_{(0, 1/2)} showed a periodic oscillatory behavior, the period of which was independent of temperature, oxide coverage and oxidation scheme, but changed in proportion to O₂ pressure. This means that all of the adsorbed oxygen atoms are associated with etching of the surface in the 2D oxide island growth as well as in the active oxidation. Based on the experimental results, a surface reaction model of 2D oxide island growth was proposed, in which (1) repeated collisions between desorption precursors SiO^* migrating on the surface lead to nucleation and 2D growth of oxide islands, (2) etching of the surface originates from oxide growth as well as SiO desorption, (3) the resultant oxide layers are enriched with Si atoms, and (4) the interfacial strain of oxide islands is rather small in comparison to that for Langmuir-type adsorption. Using the Si atom emission due to the interfacial strain as a key concept, the progress of oxidation at the interface following the Langmuir-type oxidation and 2D oxide island growth and furthermore the decomposition kinetics of very thin oxide layers can be interpreted comprehensively.