Design considerations, description, and some data on the performance are given of a large pillbox‐shaped Stark cavity absorption cell for the 1.25‐cm wavelength region. The cavity can be used in anyTE0m1mode withmranging from about 5 to about 12 and its most prominent features are: high loadedQfactor (∼5×103−104), good electric insulation (at pressures below 4×10−2mm Hg Stark voltages up to 3000 v can be applied), low Stark field inhomogeneity (diameter to length ratio 15–20), large band width (from about 18 to about 28 kMc), and low mode density. No cross‐mode resonances occur and the only undesired modes excited appreciably are theTE2m1ones. When used in transmission only theTE0m1modes couple to the output.The cavity can be used at the same time as a reference cavity of a Pound‐type klystron frequency stabilizer. The klystron frequency will then automatically follow the resonance frequency of the cavity over a frequency interval up to 400 Mc.