Abstract : The first edge illuminated SiGe phototransistor based on the available commercial SiGe/Si BiCMOS technology for low cost detector or mixer in Radio-over-Fiber applications. Its technology and structure are described. Edge mapping of the phototransistor performances, so as to observe the fastest and the highest sensitive areas of the structure, is performed. The phototransistor exhibits a cutoff frequency of 890MHz and low frequency responsivity of 0.45A/W at 850nm. This new SiGe/Si phototransistor structure provides a cutoff frequency double to the one of a top illuminated SiGe/Si phototransistor obtained using the same BiCMOS technology.