This research studied the effect of ion implantation on electrical properties of ISFETs. In the experiments the sensing membrane area were implanted with 3 types of ions (Boron(B), Phosphorus(P), and Arsenic(As)). After the implantation without annealing, the IV-characteristics of Source/Drain (P-N junction) of ISFET were performed and compared with the behaviour before implantation. In addition, the response to acid-alkaline (sensitivity) of ISFET were also studied. From the results the leakage current of source-drain, P-N junction like, decreases significantly after the implantation. However, this process damaged the devices so that the response to acid-alkaline are lost.