A sensor-on-a-chip integrated microsystem was implemented through a standard silicon (Si) complementary metal oxide semiconductor (CMOS) fabrication and an optical waveguide integration processes. The fabricated Si CMOS chip has embedded lateral pnp bipolar junction transistor (BJT) photodetector arrays and low-noise analog front-ends for signal conditioning and photodetector support. An array of parallel mixed-signal oversampled noise-shaping analog-to-digital converter (ADC) circuits was implemented as a sensor readout system. Mach Zehnder interferometric optical waveguides were post-processed on the fabricated chip surface. The electrical and optical sensitivity of the sensor Si CMOS integrated circuit signal processing components is reported herein, and optical sensitivity of 100 pW is inferred from measured data. © 2004 IEEE.