For evaluation of capacitance‐voltage measurements on an abrupt pn semiconductor junction with reverse‐biased depletion layer an approximation equation for the quantity Ue is presented, where Ue is the value at the intercept of the extrapolated plot C−2 to the applied voltage axis. The approximation formula is compared with an exact calculation. The maximum error in the approximate relationship for Ue is less than 3% in a wide range of impurity density and applied reverse voltage, therefore the discrepancy in the space‐charge layer capacitance Cs is less than 1.5%. Cs is given by the relationship, which follows from Shockley's theory, if (U + UD) is replaced by (U + Ue).