Forming of filled isolation trenches, in particular the transition area in trenches and recesses free of silicon during the realization of MEMS structures of SOI wafers. A reliable dielectric insulation of adjacent silicon regions is to be obtained. The insulation is achieved by filled isolation trenches. The end portions of the trench fill that are freed from the surrounding silicon by etching are free of conductive not completely removed silicon strips in the recess including the active sensor structure. This is accomplished by slanted wall of isolation trenches. Additionally, the trench fill should be removable at the transition area in an efficient manner. The technological realization does not require specific additional process steps.