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In this paper, without altering any step of the commercial 0.35-mum SiGe BiCMOS process, a novel photodetector named phototransistor photodetector (PTPD) has been realized and demonstrated. The PTPD shows high photoresponsivity and its structure relaxes the tradeoff between sensitivity and speed. Responsivities of 9.5 A/W for 670 nm light and of 5.2 A/W for 850 nm light were achieved. The operation details of the PTPD are introduced in this paper. The device can be readily integrated with other on-chip circuits to form a high-performance optoelectronic IC. The low cost, the high performance, and the flexibility in optical-electrical design allow the SiGe PTPD to be used in many demanding applications.