In contrast to submicrometer geometry; metal oxide semiconductor (MOS) devices which feature ultrathin gate oxides, power MOS field effect transistor (FETs) require gate oxides in the thickness regime from 50 to 70 nm. In this experiment, the effect of preoxidation surface treatments and thermal growth conditions on electrical integrity of thick gate oxides is investigated and compared with the effect on thin oxides (<15 nm). It is demonstrated that the response is relatively independent of oxide thickness when the same. temperature of oxidation is used to grow thick and thin oxides. However, when thick gate oxides of the same thickness are grown at different temperatures, the effect of metallic contaminants, namely Fe and Al, plays a decisive role in determining oxide characteristics. In the case of metal-free surfaces (HF/HCl last clean) better oxide integrity in terms of both E-bd and Q(bd) is obtained at high temperatures of oxidation (1000 and 1175C). However, in the case of starting Si surfaces contaminated with metallic impurities. (ammonia hydrogen peroxide mixture-last clean), the benefits of using a high temperature of oxidation are seen only in terms of Ebd characteristics while Q(bd) characteristics are significantly deteriorated as compared with oxides. grown at 900 degreesC.