In the last two decades, nanowire (NW) materials featuring nanoscale geometrical effect have attracted numerous attention for potential applications of highly sensitive chemical sensors and bioFETs. In the bioFET system, the mobile ion in aqueous solutions can be regarded as an important role in controlling the fundamental properties of liquid-NW interface, accordingly implying the importance of the ionic strength. Here, we demonstrated the electrical characteristics of NW FETs upon various ionic strength conditions of KCl aqueous solutions for giving more clear understanding of the effect of ionic strength on the electrical characteristics of NW bioFETs. The size of the NW width of our silicon NW FETs were defined by using the electron-beam lithography technique. In our liquid-gated bioFET system, a gold microwire was immersed in the aqueous solution for serving as a liquid-gated electrode for achieving an ideal gate-to-channel capacitive coupling system, accordingly resulting in the subthreshold swing approaching the limit value of 60 mV/dec. We also found that, when the NWs were exposed to the KCl aqueous solutions with different ionic strengths ranging from 10 μM to 0.1 M, the low-field carrier mobility decreased with increasing the ionic strength. Smaller the size of the NW width, more pronounced the decreasing trend in the mobility. This report gives insight into the importance of the ionic strength on the modulation of the electrical characteristics of NW bioFETs for chemical sensors, bioFETs, and bioelectronic applications.