This study demonstrates an electrical measurement method that analyses the properties of nanowire field effect transistors (nFETs) for biosensing applications. Detecting electrical signals is critical for all biosensing experiments especially for nFETs that are extremely sensitive to many types of environmental factors. Both direct current (DC) and alternating current (AC) measurements are frequently used. We study the pros and cons of these two methods for measuring electric signals from nFETs. Our results indicate that AC measurement generates less current data than DC measurement. However, the signal-to-noise ratio of AC measurement is higher than DC measurement. These results are important for future biosensing experiments and data analysis using nFETs.