When forming sophisticated high-k metal gate electrode structures on the basis of a threshold voltage adjusting semiconductor alloy, a highly efficient in situ process technique may be applied in order to form a recess in dedicated active regions and refilling the recess with a semiconductor alloy. In order to reduce or avoid etch-related irregularities during the recessing of the active regions, the degree of aluminum contamination during the previous processing, in particular during the formation of the trench isolation regions, may be controlled.