High-k metal gate electrode structures are formed on the basis of a threshold adjusting semiconductor alloy formed in the channel region of one type of transistor, which may be accomplished on the basis of selective epitaxial growth techniques using an oxide hard mask growth mask. The hard mask may be provided with superior thickness uniformity on the basis of a wet oxidation process. Consequently, this may allow re-working substrates prior to the selective epitaxial growth process, for instance in view of queue time violations, while also providing superior transistor characteristics in the transistors that do not require the threshold adjusting semiconductor alloy.