SiGe heterojunction bipolar phototransistors based on Si1-yGey virtual substrate have been proposed in this paper. The current gain and external quantum efficiency of the heterojunction bipolar phototransistors are calculated by solving one-dimensional diffusion equations. The computed results show that external quantum efficiency increases with the increase of Ge content of Si1-yGey virtual substrate and a high external quantum efficiency of 142 can be obtained in the heterojunction bipolar phototransistor with ten periods of Ge/Si0.4Ge0.6 multi-quantum wells on virtual substrate with Ge content of 0.6. The dependences of external quantum efficiency and current gain on structure parameters of the heterojunction bipolar phototransistors are investigated in detail. It is useful for design and optimization of the heterojunction bipolar phototransistors. (C) 2008 Elsevier Ltd. All rights reserved.