The electrical resistance of the amorphous phase gradually increases slowly with time, after switching from the crystalline state in phase‐change random‐access memory (PCRAM), which is known as the resistance drift (R‐drift). Although several interpretations of R‐drift have been proposed, the mechanisms are still not fully understood. The models are examined quantitatively by investigating the changes in the optical dielectric function and the resistance in the amorphous phase of Ge2Sb2Te5. The results suggest that R‐drift is an intrinsic phenomenon in nonequilibrium systems—the mechanical stress induced in the amorphous state relaxes into a more stable nonequilibrium state (order in disorder). Hence, R‐drift is not attributed to purely electronic processes.