A high‐temperature microwave spectrometer has been constructed for the study of hot corrosive gases. The absorption cell consists of a 213‐cmX‐band copper waveguide which is heated along roughly 130 cm of its length. A thin nickel strip held taut by stainless‐steel posts at either end of the waveguide serves as the Stark septum. The sample chamber is coupled to the Stark cell midway along its length by a slip joint formed from two concentric tubes. This design ensures a long effective absorption path length and minimizes sample consumption. The hot cell is used in conjunction with an HP 8400C microwave spectrometer source which has been interfaced to a small computer for data acquisition, storage, and retrieval. The successful operation of the spectrometer has been demonstrated with KOH vapor at 580 °C. TheJ=2←1 transitions of a number of vibrational states of monomeric KOH have been observed in the region of 32.8 GHz. The observed signal‐to‐noise ratio of these transitions indicates that the sensitivity compares favorably to spectrometers which have been used to observe higherJtransitions in the submillimeter region. Radio‐frequency–microwave double resonance techniques have been demonstrated for the first time in a high‐temperature Stark cell by observing theJ=2←1l‐doublet transitions in the (011O) state of KOH.