A device is described that enables the rapid sensing of molecules with a high degree of sensitivity and selectivity. This device is based on a depletion mode FET in which the gate electrode has been removed, certain molecular receptor species (e.g. proteins, oligonucleotides, antibodies, etc.) have been affixed, and a test solution is exposed to the gate. A counter electrode is immersed in the solution in order to establish a reference potential. Changes in the source-drain current indicate an attachment response of the system. Preliminary results are presented.