Two low phase‐noise Gunn diodeX‐band oscillators intended for use in electron paramagnetic resonance (EPR) spectroscopy are described. In the first, a 250‐mW MA49159 Gunn diode oscillator (M/A‐COM, Burlington, MA) is mounted in a coaxial transmission line that is closely coupled to a TE011transmission cavity that in turn is loosely coupled to the output transmission line. The output power is 50 mW and the phase noise is −145 dBc/Hz at 100 kHz offset. In the second, two such coaxial assemblies are used with 500‐mW MA49110 diodes for increased power. The output power is 150 mW and the phase noise is −150 dBc/Hz at 100‐kHz offset. These phase noise values are in the range of 24–29 dB better than the specification for a normal high quality klystron used in commercial spectrometers.