A technique using a coaxial diode test fixture for the mount‐independent characterization of potentially unstable two‐terminal devices is presented. A standard three‐terminal calibration procedure using reference packages is used to calibrate to the surface of the packaged device. The test fixture is designed to present a low, nonresonant impedance to the device so that measurement resolution is enhanced. The characterization of an IMPATT diode is presented as an example. © 1993 John Wiley & sons, Inc.