1. The presence of common features in the structures of crazes and SB, the possibility of their simultaneous initiation, and the same image of the time of their multiple initiation in the deformation diagrams indicate the utility of a unified approach to constructing the corresponding dependences for the creep limit of polymer materials. 2. The thermodynamic analysis of the initiation of crazing and SB as phase transitions permits obtaining an equation for the boundary surface of yielding in the stress-temperature space. The equation in the differential form is concretely defined for cases of dilatation in conditions of hydrostatic stress and biaxial loading. The results obtained are in agreement with the experimental data. 3. As a result of generalizing the relations obtained to the case of deformational processes induced by phase transitions at the boundary of nonhydrostatically stressed phases, the necessary conditions of the local equilibrium development of crazes and SB were formulated.