<p>The present invention generally relates to a vertical thin polysilicon substrate ISFET for the measurement of hydrogen ions (pH) and other ion activity in solution characterized in that wherein the present invention comprises of a method of making polysilicon vertical ISFET which is fully CMOS compatible and wherein the substrate is the polysilicon which is vertically sandwiched between a source and a drain and wherein a very high drive current is possible to achieve due to the thin polysilicon material and wherein the sandwiched structure is designed to ensure excellent noise isolation and wherein the gate lies on the same surface level as the drain and hence a very large area for better gate sensitivity is possible.</p>
