Extended-gate field-effect transistor (EG-FET) chemo- and biosensors are emerging tools for a wide range of biomedical applications. Significant efforts have been made to make them ultrasensitive to biomolecules via the development of miniaturized sensing transistors, design and optimization of extended gate sensing layer, exploration of the multiplexing ability of EG-FET configuration, and advanced data analysis. Here, we specifically focus on several important aspects related to the construction and current applications of EG-FET sensors. Namely, we review the materials, fabrication, properties of the transducer, specificities of the conditioning electronics, and signal analysis. At the same time, we discuss the current drawbacks of these sensors preventing their straightforward commercialization, such as output signal variation and non-linearities of the response. We also review the recent key applications of EG-FET sensors in the areas of early medical diagnostics, ecology, food and chemical industries, and others. Finally, we briefly discuss the future perspectives in the development of this class of sensors.