Prospects of Si/Si0.8Ge0.2 heterojunction IMPATT devices are studied through a modified simulation technique and their performances are further compared with those of homojunction devices. This high-frequency study includes the effects of mobile space charge, parasitic resistance and also considered the detrimental role of elevated junction temperature on the maximum exploitable power level from the devices. The study indicates that under similar operating condition, Si/SiGe heterojunction IMPATT is capable of delivering a RF-power output of nearly 6W (efficiency 21%), two times higher than that from Si0.8Ge0.2 homojunction diode, which is only 13% efficient. The overall study indicates the superiority of the heterojunction diodes over their homojunction counterparts as far as negative resistance, device impedance and quality factor are concerned. To the best of author's knowledge, this is the first report on highfrequency analysis of Si/Si0.8Ge0.2 heterojunction IMPATT. © 2012 SPIE.