Over the past three decades effort has been devoted to exploit the field-effect mechanism in chemical and biological sensors, due to the potential of these devices to provide large arrays of sensors that are label-free, low-cost, disposable and can be easily integrated in portable instrumentation. Most of this work concerned the development of ion-sensitive field-effect transistors. More recently, field-effect devices have been investigated for the detection of DNA hybridization and protein interactions. Of particular interest is the use of polycrystalline silicon thin film transistors. This technology is inherently low cost and yet capable of providing complex single-use microarrays.