This paper reports fabrication and characterization of ZnO nanoparticle based Field Effect Transistor (FET) device and its application for simple, rapid and label-free bacteria detection. 5 mu m FET devices were fabricated by standard UV lithography technique on Si wafers. The fabricated devices consisted of ZnO nanoparticles as channel material. Characterization of such devices resulted in threshold voltage of -2 V and trans-conductance of 1.07 mu S. The interaction between ZnO nanoparticles and bacteria sample has been exploited in this study to utilize ZnO nanoparticle based FET device to successfully differentiate between gram positive and gram-negative bacteria. Gram negative bacteria sample resulted in higher output characteristics compared to that obtained with gram positive bacteria sample. This study reports sensitivity and Limit of Detection (LOD) of 9.48 nA/CFU/mL and 776 CFU/mL respectively for gram negative bacteria and 6.96 nA/CFU/mL and 665 CFU/mL for gram positive bacteria respectively.