We have developed a method to reduce leakage current density through a SiO2 layer of Si-based metal–oxide–semiconductor structure. In this method, a ∼3-nm-thick platinum (Pt) layer is deposited on the SiO2 layer, followed by the heat treatment at 300 °C in oxygen. After the removal of the Pt layer, the density of leakage current for this structure is decreased to less than 1/1000 with no increase in the thickness of the SiO2 layer. The reduction in leakage current density is attributed to (i) a decrease in the density of defect states such as Si dangling bonds and suboxide species, and (ii) improvement of the uniformity of the oxide thickness, both of which are caused by dissociated oxygen ions injected from Pt to SiO2. © 2000 American Institute of Physics.