Time-dependent changes of electrical properties are investigated in the range of relative low heating temperatures (T = 320 to 450 K) for undoped p-CdTe grown by various methods. It is established that the character and direction of the observed changes depend on the level of uncontrolled impurities (Cu preferably), their charge state and the association degree of impurities with intrinsic (V-Cd) defects. CdTe:Ge (Sn,Pb) crystals are characterized with a high thermostability of electrical properties.