The mechanism of platinum (Pt)-enhanced oxidation of Si below 300 degrees C has been investigated by means of high-resolution x-ray photoelectron spectroscopy. When a Pt layer is deposited on the similar to 1-nm-thick silicon oxide-covered Si, low-temperature heat treatment grows the silicon oxide layer between the Pt layer and the Si substrate, while silicon oxide is formed mainly on the Pt layer in cases where Pt is directly deposited on the Si substrate. Oxidation is enhanced by the application of a positive bias voltage to the Si substrate with respect to the Pt layer during the heat treatment of the specimens with [similar to 4 nm Pt/silicon oxide/Si(100)] structure in oxygen, and in this case, a similar to 8-nm-thick oxide layer is formed at 300 degrees C for 2 h, It demonstrates that oxygen ions are the moving species in the oxide layer. The plots of oxide thickness with respect to oxidation time are linear in the oxide thickness region below 3 similar to 4 nm, indicating that the reaction at the interface is the rate-determining step. The activation energy for the interfacial reaction is estimated to be similar to 0.55 eV: much lower than that for oxidation through reaction with oxygen molecules of similar to 2 eV. The plots for the subsequent oxidation stage are expressed by logarithmic functions, showing that the migration of oxygen ions in the oxide layer is the rate-limiting process.