Si self‐interstitial diffusivities can be extracted from the diffusive behavior of certain metals (e.g., Au) in an inert annealing ambient or from the diffusion of dopant markers (typically B) under oxidizing conditions. Each type of experiment yields fairly consistent results; however, interstitial diffusivities obtained in these two ways differ greatly. The marker layer experiments rely on the assumption that the presence of the dopant does not disturb the diffusion of the interstitials, and the validity of this assumption is explored. A model of interstitial diffusivity in the presence of B is developed, two extreme cases of the B‐atom–interstitial interaction strength are considered, and the predictions of the model are compared with experiments of oxidation‐enhanced diffusion in B doping‐superlattices. From this comparison it is concluded that trapping of interstitials by B atoms in the markers cannot be responsible for the different values of the Si interstitial diffusivity reported in the literature. Further, it is shown that the presence of the dopant does not perturb the behavior of the Si self‐interstitials in the doping‐superlattices, i.e., the markers are ‘‘unobtrusive’’ probes of interstitial behavior. ©1995 American Institute of Physics.