The diffusion of arsenic and boron in oxygen-implanted SOI layers has been studied using secondary ion mass spectrometry, (SIMS), Rutherford backscattering spectroscopy (RBS), spreading resistance profiling (SRP), and transmission electron microscopy (TEM). A SIMOX (separation by implantation of oxygen) was produced, and then a 27-nm oxide layer was grown prior to implantation of either arsenic (80 keV, 5×10¹⁵ cm^-2) or boron (15 keV, 2×10¹⁵ cm^-2). The samples were annealed at 900°C for 10 min, 30 min, and 120 min in an inert ambient and analyzed using the above techniques. The experimental results have been compared with process modeling simulations where diffusion behavior appropriate to bulk silicon has been incorporated. It has been found that by using appropriate implant and anneal schedules it is possible to produce SIMOX material where the quality of the silicon overlayer allows the majority of diffusion behavior to be predicted using such models.