In low-dose separation by implanted oxygen (SIMOX) the concentration of implanted oxygen is less than the SiO2 stoichiometry even at its peak depth. The fabrication process, therefore, consists of oxygen precipitation, growth, and coal lescence of the precipitates during a high-temperature anneal. It has been believed that there is a process window of 4 +/- 0.5 x 10(17)/cm(2) for the oxygen dose to form a continuous buried oxide in low-dose SIMOX. However, it may be possible to extend the dose window by applying the proper annealing sequence for each dose. In this study, we succeeded in extending the dose window to 2-6 x 10(17)/cm(2) by modifying the temperature ramp rate depending on the dose for the high-temperature anneal, based on thermodynamical considerations.