The present invention relates to semiconductor-on-insulator (SOI) substrate structures that contain surface semiconductor regions of different crystal orientations located directly on an insulator layer. The present invention also relates to methods for fabricating such SOI substrate structures, by growing an insulator layer directly on a multi-orientation bulk semiconductor substrate that comprises surface semiconductor regions of different crystal orientations located directly on a semiconductor base layer, and removing the semiconductor base layer, thereby forming a multi-orientation SOI substrate structure that comprises surface semiconductor regions of different crystal orientations located directly on the insulator layer.