A high temperature thermal cavity system, designed for material and material‐environment studies, is described. A cylindrical cavity (17.4 mm diam and 25.4 mm long) is formed by a 2 mm thick vitreous carbon tube and two vitreous carbon end plugs. Provisions were made on the vitreous carbon tube and end plugs for temperature and mass spectrometric measurements and for admittance of environmental gases. The thermal cavity is resistively heated to 2000 K at an input power level of 2.5 kW with a partially open, four‐layer molybdenum heat shield. Higher temperatures are obtained with a smaller cavity. The design of the thermal cavity, the temperature performance of the cavity, the change in electrical resistance of the vitreous carbon at high temperatures, and the mass spectrometric analysis of vitreous carbon‐oxygen reaction are discussed.