Experiments have been performed to measure the parameters of epitaxial GaAs cavity controlled Gunn oscillators with

cm
-2over the frequency range of 7 to 20 GHz. It is found that individual devices exhibit a large variation of transit frequency with bias voltage and this is related to their performance in a cavity. The real and imaginary parts of the device reactance under cavity controlled operating conditions and the RF voltage swing across the device have been measured. These are discussed in the light of presently available analytical theories.