The incorporation and redistribution of oxygen in silicon after zone melting recrystallization of Si on SiO 2 has been studied in detail using secondary-ion mass spectrometry. The oxygen profile can be characterized by a depletion at the Si-SiO 2 interfaces because of the oxide formation at the interface and a diffusion from oxygen out of the supersaturated film towards the interface. Exact determination of the oxygen concentration at the interfaces is complicated by oxygen adsorption during the analysis, sample charging as the underlying oxide is approached and by the initial surface roughness of the recrystallized silicon. A model has been derived which predicts the shape of the oxygen profile in the recrystallized layer as well as in the substrate. The profile measured in the supporting wafer agrees with the model of subsequent in- and outdiffusion of oxygen during the thermal cycling.