Dutch engineer Piet Bergveld studied the MOSFET and realized it could be adapted into a sensor for chemical and biological applications.
In 1970, Bergveld invented the  ion-sensitive field-effect transistor (ISFET). He described the ISFET as "a special type of MOSFET with a gate at a certain distance". In the ISFET structure, the metal gate of a standard MOSFET is replaced by an ion-sensitive membrane, electrolyte solution and reference electrode.
ChemFETs are based on a modified ISFET, a concept developed by Bergveld in the 1970s. There is some confusion as to the relationship between  ChemFETs and ISFETs. Whereas an ISFET only detects ions, a ChemFET detects any chemical (including ions).