We use microelectronic techniques to fabricate silicon nanowires field effect transistors (SiNWs-FET). The source-drain current versus the voltage curve shows that the contact pad and the silicon nanowire form an ohmic contact. 3-aminopropyltriethoxysilane (APTES) is used as interfacing molecules, and assembly of these molecules is essential in surface modification technologies. Then we modified biotin on SiNWs-FET to detect streptavidin. For SiNWs-FET, variation in molecular charge is reflected in a change in the wire current. The response of the drain-source current of biotin-modified SiNWs-FET to changes in streptavidin concentration was measured by using a lock-in technique. Control experiment was carried out before biotin modified, and the SiNWs-FET did not exhibit a current change when 10-7 M streptavidin passed through the microfluidic channel. This demonstrates that the APTES does not react to streptavidin. And in the present concentration-dependent real-time measurement of biotin modified SiNWs-FET, the detection limit of streptavidin is 10 -8 M.