The stability against crystallization of the amorphous phase-change materials Cu x Ge 50 − x Te 50 (CGT) exhibits an unusual behavior at low Cu concentrations with x ≈ 15 being the most stable composition. Three CGT compositions with x = 5 , 15, and 25 are analyzed using extended X-ray absorption fine structure (EXAFS) at the Ge-K, Cu-K, and Te-K edge at 10 K. EXAFS analysis shows that the average coordination number (CN) increases with the Cu concentration from 2.8 at x = 5 to 4.0 at x = 25 . Cu-EXAFS spectra indicate the formation of Cu clusters for low Cu concentrations ( x = 5 and x = 15 ). The existence of these clusters is further analyzed by X-ray absorption near-edge structure calculations, supporting small polyhedral and/or disk-like Cu clusters which are linked to the surrounding amorphous GeTe matrix via CuTe bonds. Hence, the GeTe network is Te enriched, leading to a maximum of GeTe bonds at x = 15 . As a result, this establishes an amorphous network which is stabilized against crystallization.