When DNA strands bind to the gate surface of ISFETs, changes in surface potential occur due to the negative charge of DNA, thereby allowing for excellent performance of in DNA sensing. Through special treatments of the oxide layer of a FET, probe DNA can be immobilized onto the oxide surface in an orientation-controlled manner. As for methods of DNA detection, the most widely used techniques depend on enzymatic, fluorescent, and radiochemical tags. But all these methods, though they show high sensitivity and low detection limits, are insufficient to solve problems such as assay time, cost and complexity. To overcome these drawbacks, a label-free detection of DNA using a FET device with a real-time electrical readout system for rapid, cost-effective, and simple analysis of DNA Sensors 2009, 9 7115 samples has been proposed [8]. As an example of this, a detection platform based on an amorphous silicon-based (a-Si:H) ISFET for the label-free detection of covalent immobilization of DNA and subsequent hybridization of its complementary DNA was developed by Goncalves et al. In this study, DNA binding behavior was monitored using an ISFET biosensor, which was observed as changes in the threshold voltage (VTH). Through electric field monitoring, a sensitive response of a-Si:H ISFET to target DNA of different levels of hybridization was observed. Since the theoretical basis for elucidating the electronic data obtained from ISFET measurements is not strong, except for several parameters such as charge effect, capacitance effect, etc., a detailed study about the true behavior of thin-film FET biosensors will help to develop an advanced ISFET device suitable for real sample detection