This paper analyzes the design tradeoffs between Si and SiGe MITATT diodes using a Monte Carlo method, The narrow bandgap material Si0.7Ge0.3 improves the charge confinement in the avalanche generation region and therefore increases the RF power generation efficiency. A SiGe MITATT diode operating at 200 GHz can produce 42 mW of RF power which is 63% higher than that from a Si MITATT diode. Beyond 300 GHz, the superior thermal properties of Si allow the Si MITATT diode to be driven at higher DC power level. Therefore, 2.3 mW can be generated from the Si MITATT diode at 400 GHz but only 1.5 mW from the SiGe MITATT diode. (c) 2007 Published by Elsevier Ltd.