Optical sensors have been found in numerous measurement applications for scientific instrumentation and spectrometers. To achieve a high gain, devices such as photomultiplier tubes (PMTs), avalanche photodiodes (APDs), and phototransistors are commonly used. PMTs with high gain of >105 are bulky and have high power consumption. Compact APDs tend to have high shot noise and strong temperature dependence. Phototransistors taking advantage of current amplification of bipolar junction transistors (BJTs), on the other hand, do not require high electric field to attain a gain of 10–100. Here, this work addresses a new optical sensor design with an adjustable gain from 1 to 106 and a wide dynamic range over 160 dB. The sensor is based on light-modulated body-bias effect and can be manufactured by commercial CMOS technology.