This letter presents the design, measurement results, and modeling formula of a P-well/deep N-well photodetector (PD) realized in a standard 65-nm complementary metal-oxidesemiconductor without process modification. With 0.5-V reverse bias (V PD ), the measured dc responsivity to an 850-nm light source is 51 mA/W and the −3-dB bandwidth is 500 MHz. Besides, a seamless cosimulation of the PD and the following receiver circuits are presented. Optical measurement results show that under 0.5-V V P D , the optical receiver achieves a new record data rate of 9 Gb/s for 2 15 -1 pseudorandom binary sequence with 10 −12 bit error rate and −4.2-dBm optical input sensitivity.Index Terms-CMOS photodetector, responsivity, frequency response, CMOS integrated optical receiver.