compressively strained SiGe-On-Insulator (SGOI) made by the Ge-condensation technique is used as a performance booster for ultrathinfully depleted silicon-on-insulator transistor technology. Here, we report on the evolution of the compressive strain in the SiGe film alongthe formation of local SGOI. For this, experimental maps of lattice strain with nanometer spatial resolution have been obtained by dark-fieldelectron holography and compared to results from numerical models describing the mechanics of the structures. In particular, we report onunexpected strain evolutions when the top semiconductor layer is patterned to fabricate the shallow trench isolations that separate the SinMOS from the SiGe pMOS areas. Dramatic and long-range relaxation of the compressive SiGe layers occurs, while no extended defects areformed in the crystal. The phenomenon involves relative horizontal displacements between the SiGe layer and the underlying Buried Oxide(BOX). We suggest that the Ge-enrichment of the layer close to this interface by the Ge-condensation technique modifies the SiGe/BOXinterface and that strain relaxation results from the propagation of some interfacial defects from the edge to the center of the structure, drivenby the shear stress at the interfa