The various embodiments herein provide a method for fabricating Ion-Selective Field-Effect Transistor (ISFET) with a nano porous poly silicon layer on a gate region. The method includes providing a p-type silicon substrate and forming a silicon dioxide layer on the p-type silicon substrate. A poly silicon layer is deposited on the silicon dioxide layer. The poly silicon layer is patterned to form a gate region, a source region and a drain region in the silicon dioxide layer. A passivation layer is deposited on the gate region, source region and the drain region. The passivation layer is etched using a buffered HF to transform the poly silicon layer into a nano porous layer on the gate region by a sequential reactive ion etching process.