An apparatus for applying uniaxial stress >109Pa at temperatures of 20–300 K is described. The apparatus is used with a deep level transient spectroscopy (DLTS) experiment, but it has more general applications. We have used this apparatus to observe the splitting of a DLTS defect level atEc−0.17 eV in neutron irradiated silicon and have determined from the splitting, as a function of stress orientation, that the defect symmetry is consistent with the oxygen‐vacancyA‐center.