<div> Semiconductor gas sensors are increasingly being used as gas detectors for applications such as gas-leak alarm, process control and pollution control. Researchers have attempted to meet the demand for higher sensitivity and selectivity of devices by modifying the properties of the semiconductor gas sensors. This has mainly been achieved by developing fabrication methods such as thin and thick film techniques, the addition of transition metals onto sensors and more recently, nanostructuring materials. The book begins with an introductory review of resistor and non-resistor types of sensor, conduction mechanisms, electrode materials and electrode-oxide interfaces. The second part introduces recent developments in silicon carbide and graphene-based gas sensors, wide bandgap semiconductor gas sensors, micromachined and direct thermoelectric sensors, while part three discusses the use of nanomaterials, including metal oxide nanostructures, quantum dots, single-walled carbon nanotubes and porous silicon. The conclusion surveys key applications in environmental monitoring, detecting chemical warfare agents and monitoring gases such as carbon dioxide.</div>