A PbTiO.sub.3/SiO.sub.2-gated ISFET device comprising a PbTiO.sub.3 thin film as H.sup.+-sensing film, and a method of forming the same. The PbTiO.sub.3 thin film is formed through a sol-gel process which offers many advantages, such as, low processing temperature, easy control of the composition of the film and easy coating over a large substrate. The PbTiO.sub.3/SiO.sub.2 gated ISFET device of the present invention is highly sensitive in aqueous solution, and particularly in acidic aqueous solution. The sensitivity of the present ISFET ranges from 50 to 58 mV/pH. In addition, the disclosed ISFET has high linearity. Accordingly, the disclosed ISFET can be used to detect effluent.