An EOSFET or electrolyte–oxide–semiconductor field-effect transistor is a FET, like a MOSFET, but with the metal replaced by electrolyte solution for the detection of neuronal activity. Many EOSFETs are integrated in a neurochip. An EOSFET or electrolyte–oxide–semiconductor field-effect transistor is a FET, like a MOSFET, but with the metal replaced by electrolyte solution for the detection of neuronal activity. Many EOSFETs are integrated in a neurochip.