In a mesa isolation configuration for forming a transistor on a semiconductor island, an additional planarization step is performed to enhance the uniformity of the gate patterning process. In some illustrative embodiments, the gate electrode material may be planarized, for instance, on the basis of CMP, to compensate for the highly non-uniform surface topography, when the gate electrode material is formed above the non-filled isolation trenches. Consequently, significant advantages of the mesa isolation strategy may be combined with a high degree of scalability due to the enhancement of the critical gate patterning process.