Oxygen precipitates (OPs) formed by the annealing of oxygen implanted silicon samples at diverse temperatures in the ranges from 700°C to 1100° have been investigated with capacitance-voltage and transmission electron microscopy techniques. An increase of the OP sizes with the increasing temperature was found to accompany with a decrease of the OP embedded positive charge being inversely proportional to the formers. The obtained result showed that the positive charge is localized in SiO_x shell of predominantly stoichiometric OP core.