Strained silicon on insulator (SSOI) technology has emerged as an attractive option for the introduction of wafer-scale strain into upcoming CMOS technology nodes. Two key breakthroughs which have made this possible are discussed in this paper. First, the development of SSOI without a SiGe layer in the final wafer has eliminated significant CMOS process integration challenges. Second, the discovery that strained films well in excess of the critical thickness can be used for SOI MOSFETs has paved the way for applying SSOI to mainstream partially-depleted applications. To understand ultimate thickness limits, we explore strain retention via X-ray diffraction measurements on strained-Si/relaxed-SiGe donor wafers with Ge contents from 14 to 33%. We show that strained silicon can be grown to over 15 times the critical thickness before gross relaxation occurs. This surprising result suggests that extremely high strain levels will be attainable for future generations of SSOI devices.