Structural phase transitions of the B1-B2 type in alkali halide crystals are investigated at a temperature other than 0 K. The pressure of B1-B2 phase transition is calculated as a function of temperature. The calculated pressure of B1-B2 transition in these crystals is weakly and almost linearly dependent on temperature. For a number of ionic crystals, the p 0 (T) curve has a maximum at some value of temperature.