Open-gate Si-based ion-sensitive –eld-effect transistors (ISFETs) were proposed for use as pH sensors by Bergveld in 1970. These transistors are promising device structures for integrated chemical and biological sensors [1]. A gate voltage induced by ions adsorbed onto the open-gate region modulates the surface space-charge layer underneath and results in the change of the source-drain current, thus realizing the operation of ISFETs. To improve the relatively insensitive response and poor stability of the original ISFET structure, various sensing materials, such as Si3N4 [2], Al2O3 [2], or Ta2O5 [3], were investigated to substitute the role of silicon oxide. Moreover, materials with more robust surface properties are particularly required for chemical and biological sensors against possible damages and contaminations from harsh sensing environments.