It has been observed that considerable discrepancy occurs between total As in Si diffusion profiles obtained by Irvin's curve and those determined by neutron-activation analysis. This discripancy can be explained in terms of the formation of inactive [VSiAs2] complexes. Under conditions of equilibrium between As+ ions and [VSiAs2] complexes, it is possible to derive the relation-relationship between total As, CT, and bulk resistivity, ρ, by using Irvin's curve as a standard. It is shown that a single CT-vs-ρ curve is not sufficient because of the temperature and initial Si substrate dopant dependence of [VSiAs2] complex formation. Equilibrated near-Si-surface As data obtained by activation analysis and resistivity measurements are presented to verify the theory. Excellent agreement is obtained. The important result of this study is that it is now possible to determine partially the As CT(x) diffusion profile from four-point probe measurements and anodic sectioning of the Si. While this technique can only be used over approximately the first 50% of the diffused layer, the rest of the CT(x) profile can be estimated from the electrically active As profile, CA(x) (determined by Irvin's curve) and an equation relating CT(x) to CA(x). © 1973 American Institute of Physics.