The temperature dependence of minimum yield and dechanneling coefficient is studied for <110> and <111> axial channeling in germanium and silicon crystals. The observed minimum yield and the dechanneling coefficient are represented by linear relations of the mean square amplitude of thermal vibrations, and the results are compared with theory. For the minimum yield, the observed values are independent of energy and kind of particles and agree with theoretical values. The dechanneling coefficients show a poor agreement with theory. To find a reason for this discrepancy, the critical angle and the theoretical treatment are considered and discussed.