Oxygen has been diffused into silicon at temperatures above 1250°C. The diffused layers have been detected by subjecting the samples to a second heat treatment at 450°C. The donors, which then form from the oxygen, cause the layer to convert tontype. The relationship between donor and oxygen concentrations was established by studying donor formation in crystals of known oxygen concentration. From these results and the electrical properties of the layers, the diffusivity and solubility of oxygen in silicon has been measured. For silicon, in contact with SiO2(glass), the heat of solution is (2.3±0.3) ev and the diffusivity is given byD=135exp(−3.5 ev/kT).