Authors derived an electromagnetic theory of the contactless measuring method of electric conductivity of nonmagnetic semiconductor circular wafer referring to the arrangement shown in Fig. 1, and have got the result for d'd:(16)where V is electromotive force induced along measuring coil due to the eddy current in the wafer induced by exciting coil, for the lower frequency range:f50 MHz, λ6 m, for R 1 m (1')where R is a symbolic representation of scale of arbitrary element used in this arrangement, and under the condition that the thickness t of the wafer is much smaller than the depth of penetration δ of the semiconductor. We discussed practical measurement of V, especially separation of V and V0 which is electromotive force induced by direct field from exciting coil to measuring coil, using the phase difference between V and V0. We use SI unit system and time factor ejwt in this paper.