Semiconductor-on-insulator (SOI) substrates including a buried oxide (BOX) layer having a thickness of less than 300 Å are provided. The (SOI) substrates having the thin BOX layer are provided using a method including a step in which oxygen ions are implanted at high substrate temperatures (greater than 600° C.), and at a low implant energy (less than 40 keV). An anneal step in an oxidizing atmosphere follows the implant step and is performed at a temperature less than 1250° C. The anneal step in oxygen containing atmosphere converts the region containing implanted oxygen atoms formed by the implant step into a BOX having a thickness of less than 300 Å. In some instances, the top semiconductor layer of the SOI substrate has a thickness of less than 300 Å.