Ge-rich Sil-xGex nanocrystals are formed by the selective oxidation of Si during the dry oxidation processing of an amorphous Si0.7Ge0.3 layer. The oxidation kinetics of the alloy film in the temperature ranges from 600 to 800 degreesC are well explained by the classical model proposed by Deal and Grove with the activation energies of the linear rate and parabolic rate regime of about 1.35 and 1.02 eV, respectively. As a result of the selective oxidation process, Ge-rich Sil-x,Ge-x nanocrystals are formed with the size of 5.6 +/- 1.7 nm and with the spatial density of 3.6 X 10(11)/cm(2) at 600 degreesC. With an increase of the oxidation temperature to 700 and 800 degreesC, the size of the nanocrystal is increased to about 20 nm. The variation of size of the nanocrystals as a function of temperature is explained considering the solid phase crystallization of amorphous film, oxidation rate, and grain growth.