Thermal stability of the Al-alloy reflective layer is essential for the archival life of a rewritable phase change optical disk. The new Al-l-lf-Pd alloy reflective layer provides excellent thermal stability A disk using this Al-alloy and a Pd-Ge-Sb-Te alloy recording layer is extremely stable. The bit-error-rate (BER)of the recorded signal did not change substantially after an acceleration test of 6,800 h under the conditions of 90 degrees C, 80%RH. X-ray diffraction analysis showed that the nem additive components (Hf,Pd) of the Al-alloy prevented the growth of the Al crystals.