Integrating multiple gate oxides on a same die requires a proper definition of their respective active area (fig. 1). First the thick gate oxide is grown, and covered by some photoresist. Then a wet etch removes this oxide on the die areas where the resist has been developed. Finally, after resist stripping and surface cleaning, the thin gate oxide is grown. The interaction between the thick oxide surface, the resist and the etchant makes the wet etch challenging. This paper deals with some characterizations and solutions to improve this process.