A novel silicon nanowire field effect transistor (SiNW-FET) was fabricated using complementary metal oxide semiconductor (CMOS) compatible technology. The shrank nanowire with high surface-to-volume ratio and individual back gate were achieved by the local-oxidation of silicon (LOCOS) process. The width of nanowire by this technique can be shrank down to sub 100, nm. The drain current versus gate voltage (Id-Vg) characteristic of the SiNW-FET exhibits about five orders of magnitude of Ion/Ioff current ratio, and the threshold voltage shifts positively after hybridization of 1fM concentrations of HBV X gene DNA fragments and 3, ng/mL concentrations of the cancer marker, respectively. The results show that the back-gated nanowire device has the capability of acting as a real-time, label-free, highly sensitivity and excellent selectivity SiNW-FET biosensor in detecting biomolecules.