A special test structure consisting of a box‐shaped boron profile capped by a lightly doped arsenic layer has been used to determine that extended defects absorb some of the interstitials injected during a wet thermal oxidation. Reduced oxidation‐enhanced diffusion of the boron layer is observed for samples containing the extended defects. Secondary ion mass spectrometry measurements are combined with transmission electron microscopy measurements to calculate theDIC*Iproduct which is found to be in good agreement with values previously obtained from gold diffusion experiments. In addition, a lower bound on the ratio of the net number of silicon atoms injected during the oxidation to the number of silicon atoms consumed is calculated. A one‐dimensional model for the growth of the extended defects has been implemented intosuprem‐iv. Simulations with the new model agree with experimental data. The growth of the extended defects is also shown to be a reaction‐limited process.