A sensor for detecting the presence of predetermined chemical/biological molecules, the sensor having a MOSFET device (2, 3, 6, 7, 9, 10, 12, 13), the gate having an array of nanoscale fingers (6,7), and on fingers or in spaces between the fingers, chemical/biological receptor molecules (15) suitable for selectively binding with the predetermined chemical/biological molecules, the sensor also having circuitry (4, 5, 11, 12) for measuring a change in a change in drain current of the FET caused by the predetermined chemical/biological molecules becoming bound to the receptor molecules. Sensitivity and reliability can be increased compared to capacitive sensors.