The development of TRAPATT diodes for long-pulse operation (10 to 100 µs), high duty cycle (1 to 15 percent), and wide bandwidth (12 percent), for phase array systems at

band requires new device fabrication and new heat-sinking technology. A novel TRAPATT diode in the form of interconnected long strips having high periphery-to-area ratio (cruciform) has been designed and fabricated. In this paper we described the thermal properties of the cruciform structure diode, which sustains 50-µs pulse width at 5.5-percent duty cycle while delivering 68-W RF power at 5-dB gain and 9-percent added efficiency, in addition to 100-µs pulse width at 4.2-percent duty cycle while delivering 50-W RF power output ast 3.6-dB and 5.5-percent added efficiency, both as narrow-band amplifier.