The effect of implantation dose on microstructural development of the buried oxide (BOX) of 200 keV oxygen implanted Si was studied by electron microscopy. A continuous BOX layer with a low density of Si islands was obtained for a dose of0.45×1018 cm−2, following high temperature annealing. At a lower dose of0.225×1018 cm−2a layer did not form, but only disjointed, isolated, oxide precipitates developed. At a higher dose,0.675×1018 cm−2, a continuous BOX layer with a high density of Si islands formed. Microstructures of intermediate-temperature annealed samples showed the formation of oxide precipitates at preferred depths, the morphology being dose dependent. The final microstructure of the BOX is strongly influenced by the evolution of the oxide precipitates during annealing. A qualitative mechanism is proposed for the dose-dependent behavior of BOX formation during the annealing process. ©1997 American Institute of Physics.