We investigate a bio-molecule sensing scheme where the conducting channel of a functionalized nanowire (NW) field-effect transistor (FET) can be gated by the presence of a charged analyte. The favorable geometry of these NW sensors leads to a promise of single molecule detection sensitivity. Although sensor devices based on NWs have been demonstrated and their basic operating principles have been realized, sensor sensitivity and selectivity remain important areas of ongoing study. There are two elements that determine the sensitivity of these devices: the device noise and the signal size for single molecule detection. These factors can be combined to determine a sensor’s sensitivity number, i.e. the lowest number of molecules that can be detected. We present noise measurements performed on bioFET devices that demonstrate this sensitivity metrology. Test structures were fabricated with c-axis MBE grown GaN NWs that are described at length elsewhere<SUP></SUP>. Nanowires were released from their growth substrate into isopropanol via ultrasonic agitation, forming a suspension of wires that was then pipetted and aligned using dielectrophoresis onto photolithographically-deposited Ti pads. The resulting two-terminal bridge structure was capped with a layer of Ti/Al, pinning the wires to the substrate and forming two conformal electrical contacts. A protective SiN<SUB>x</SUB> hard mask was deposited over the entire device, and functionalization windows above the NW surface were etched. We measured the current noise spectrum by applying a voltage to our device in series with a measurement resistor, whose resistance was approximately matched to the device resistance. The voltage across the device alone (V<SUB>bias</SUB> = 1.0 V) was offset, amplified, and filtered before being measured by a spectrum analyzer. Using the known circuit resistance values the measured voltage noise was converted to current noise. The current noise spectral density, S<SUB>I</SUB>, followed a 1/f frequency dependence. Using the parametrization of S<SUB>I</SUB> = B<SUP>2</SUP>/f we found that B = 8x10<SUP>-10</SUP> A. The contribution to the channel current from a single carrier induced by a single surface charge is ΔI<SUB>1</SUB> ≈ μeV<SUB>bias</SUB>/L<SUB>2</SUB>. Here μ, e, and L are mobility, single charge, and wire length. Using μ = 500 cm<SUP>2</SUP>V<SUP>-1</SUP>s<SUP>-1</SUP> <SUP></SUP> and L = 5.8 μm we found ΔI<SUB>1</SUB> = 0.2 nA. The value of B needed for single molecule detection is B<SUB>1</SUB> = 0.2ΔI<SUB>1</SUB> = 4x10<SUP>-11</SUP> A<SUP></SUP>. The sensitivity number of our device, which is the ratio of the measured B coefficient and B<SUB>1</SUB>, was therefore 20. The noise level of shorter devices has yet to be investigated, but this is one possible approach to improving device sensitivity toward single-molecule detection.