The crystallization of the amorphous Ge2Sb2Te5 film was investigated by in situ electrical sheet resistance measurement. The crystallization start temperature increases logarithmically with heating rate and is equated. The effective activation energy E-A of the crystallization is 2.34 eV at slow heating rates below 40 degrees C/min and decreases to 0.49 eV at higher heating rates because of the reduced activation energies for both nucleation and growth of the crystalline face-centered cubic phase by overheating at high heating rates.