Reactive ion etching of Si and SiO2in SF6plasmas in which the samples are mounted on a liquid‐nitrogen‐cooled electrode has been studied. At this temperature SF6condenses on the electrode surface, but it is possible to maintain a plasma. Si etch anisotropy has been demonstrated at low temperature, in agreement with previous studies. Mass spectrometry and optical emission spectroscopy indicate that fluorine is the dominant species in the plasma because SF6and SFxspecies are removed from the gas phase by condensation.