Phenomenological crystallographic theory of martensitic transformation was applied to the phase transition of PRAM (phase‐change random access memory) Ge2Sb2Te5 alloy for the first time. The speedy structural transition of Ge2Sb2Te5 from cubic to hexagonal phases could be well described by a shearing transformation from cubic {002} to hexagonal {‐113} besides the removal of vacancies. This model shows good consistency with crystallographic models, X‐ray diffraction analysis, ab initio total energy and density‐functional theory calculations of Ge2Sb2Te5.