Hydrothermal annealing experiments have been performed on samples of the Sharps meteorite in order to investigate the mechanism responsible for the metamorphism‐related, 105‐fold range in the thermoluminescence (TL) sensitivity in ordinary chondrites. Duplicate 50 mg samples of meteorite were annealed under the following conditions: (a) 168 h at 785°C and 1 kbar; (b) the same time, temperature and pressure, but with 2 wt% water; (c) 174 h at 855°C and 0.77 kbar with 2 wt% water and 2 molal sodium disilicate (NadiSi); (d) the same time, temperature and pressure as the preceding samples, but with 10 wt% H2O and 2 molal NadiSi. Samples annealed under the first three sets of conditions showed little or no change in their TL sensitivities, however the samples annealed with 10 wt% water and 2 molal NadiSi showed a 3 to 10‐fold increase in TL sensitivity, and the temperature of the TL peak was suggestive of feldspar in the high‐temperature form. We suggest that these data are consistent with the TL sensitivity‐metamorphism relationship in ordinary chondrites being due to the formation of the TL phosphor, feldspar, by the crystallization of chon