The authors report on fabrication and hydrogen separation performance of an array of thin, freestanding Pd/Ag alloy membranes. Film deposition from an alloyed sputtering target results in robust film characteristics. Long-term stability of the membranes has been demonstrated with experimental testing at temperatures of 473–627 K. Within the testing period the membrane has withstood more than 30 thermal cycles by returning to ambient temperature between subsequent tests. Throughout the long-term testing, hydrogen permeation levels have increased by more than a factor of 2. Electron microscopy of the membranes indicates that performance enhancement is due to microstructural changes which are promoted at elevated temperatures.