The rates of material reactions in Al/Pd2Si/Si junctions have been measured as a function of time between 200 to 350°C. Using an Auger sputter profiling technique, the kinetics and activation energies for Pd and Si diffusing into Al and the penetration of Al into Pd2Si were determined. The results can be correlated to the overall phase stability of the system and to the changes in the electrical characteristics of the Schottky junction. The mechanism of junction degradation and the role of Pd2Si are discussed. The present results reveal some basic limitations on the stability of this junction at elevated temperatures.