The operating life for a newly developed millimeter-wave silicon DDR IMPATT diode, which is hermetically sealed in a mechanically rugged miniature ceramic package with a diamond heat sink, is evaluated by accelerated life tests consisting of high-temperature storage and high-temperature DC operation. A mean time to failure (MTTF) value of approximately 2.6105 h (3800 FIT) is predicted at a junction temperature of 235, where the diode is capable of delivering an output power of 100 to 150 mW at 80 CHz band. The predominant failure mode is a junction short caused by gold diffusion into the silicon layer. An rf operating life test is also conducted. There has been no failure for 12,000 h.