Complementary Metal-Oxide-Semiconductor (CMOS) based sensor systems continue to play an important role in various biomedical, chemical, industrial, food safety, national security and defense, and environmental applications. This is because CMOS fabrication processes would allow one to produce miniaturized systems with low cost, low power and mass-producibility. This book introduces the author's research work done in Sensor Microsystems Laboratory at McGill University which involves the development of integrated CMOS optical and CMOS electrochemical sensor microsystems for biochemical sensing applications: oxygen and bacteria detection. In future, based on the principles and prototypes discussed in this book, novel sensor microsystems can be developed for different biochemical sensing applications in the manner of smaller size, lower cost and equivalent/better performance compared to conventional available instruments.