The advancement of chemical sensors to meet needs in automotive, environmental and process control applications has generated much interest in recent years. These applications demand a sensor that has a relatively small size, high sensitivity, low energy consumption and modest cost. Silicon-based microfabrication and micromachining processes show promise for the manufacture of chemical sensors that meet these criteria. These processes include photolithographic reduction, thin film metallization, reactive sputtering, and chemical, anisotropic and plasma etching. These techniques can be used to produce a three-dimensional sensor with a geometrically well-defined configuration. A thin membrane and suspension bridge sensor structure results in a low mass-heat loss and low energy consumption device. The sensitivity and selectivity of the sensors are also enhanced by using a differential mode of operation and at an elevated temperature. Microfabricated chemical sensors, including tin or other metal oxide based, Schottky diode, solid electrolyte electrochemical and calorimetric devices, will be discussed.