This project was done in cooperation with the TE-EPC-LPC section at CERN. They were experiencing failures in one of their power converter from the rectifying power diodes, and were interested in finding the reason for the failure. They were observing a high leakage current in some of the diodes. The purpose of this project was therefor to investigate the reliability of a diode, and its different failure mechanisms. Diodes can fail from multiple mechanisms some of which can be detected under operation of the diode, in this project the possibility of predicting the lifetime of the diode from its reverse leakage current was investigated. CERN suspected that the failure was either due to avalanche currents in the device or because thermal cycling in the device. Therefor was a non-repetitive avalanche current test, repetitive avalanche current test and a power cycling test performed on the diode. The non- repetitive avalanche current test gave no failures, proving that single event avalanches were not the reason for failure. In the repetitive avalanche current test the diodes was crashed, but no connection between leakage current and time before failure could be observed. In the power cycle test it was observed that failure was induced much faster in a diode with a much higher reverse leakage current than another.