The impurity profile of an epitaxial layer has been determined from the capacitance-voltage ( C-V ) characteristics of a diffused p-n junction. The C-V characteristics were corrected for peripheral and diffused layer effects. Peripheral capacitance corrections account for the lateral spread of the space-charge region, whose periphery is assumed to be cylindrical. Diffused layer corrections account for the penetration of the space-charge region into the diffused layer, assumed to be Gaussian. The importance of these corrections can be estimated from graphs that cover a wide range of practical diffusion conditions and junction diameters. The sensitivity of profiles to the assumed Gaussian diffusion are examined. Finally, the corrections are applied to an experimental junction and the results are presented from a computer printout. The Appendix includes graphs for determining the space-charge width of a Gaussian-diffused silicon junction, given the diffused layer sheet resistance, junction depth, and background concentration.