Microwave conductivity of semiconductors determined from transmission or reflection of the dominant mode of rectangular waveguide may contain a significant error caused by the impedance of the contact between the sample and the broad waveguide wall. This error increases with increasing bulk conductivity. The present paper describes a technique which eliminates this source of error by utilizing the TE01° mode of circular waveguide in a ``reflection coefficient bridge.'' Measurements of intrinsic germanium at 48 GHz show no contact influence over the conductivity range between 2 and 2×103mho/m. In contrast, the conductivity measured with a conventional rectangular waveguide transmission bridge saturates at about 50 mho/m.