A parallel‐plate Stark cell giving a very homogeneous electric field is described. It can be used either for Stark spectroscopy in the infrared and microwave ranges or in infrared–microwave double resonance experiments. Microwave absorption lines, 12.600 GHz frequency shifted, have been observed; it is more than 36 times as much as earlier displacements obtained with such cells. For pressures up to 30 mTorr, a suitable device keeps the breakdown voltage always above 10 kV, corresponding to an electric field of 50 kV/cm.