Traps in the ZnO TFTs affect the electrical characteristics of the device in general and threshold voltage (V_T) in particular. They are mostly due to the disordered nature of the deposited semiconductor channel as grain boundary traps or traps originated at the ZnO and gate-dielectric interface[1]. The distribution of grain boundary and interface traps is assumed to be Gaussian within the energy bandgap of ZnO [2], [3]. It was observed that as the acceptor-like trap density increases the threshold voltage (V_T) of TFT increases and the subthreshold swing degrades. Also, the location of the peak trap concentration with respect to E_C affects V_T. Deeper the location of the peak within the energy bandgap of ZnO more is the change in threshold voltage (V_T). Fig. 1 show the schematic diagram of TFT and Fig. 2 represents the energy of conduction band edges (E_C) in the presence of GBs. Fig. 3 shows the plot of Gaussian trap density vs. energy bandgap. Fig. 4 depicts the transfer characteristics of ZnO TFT for varying peak concentration (N_a) for GB=10. As trap density increases from 1⨯10¹⁰cm^-2eV^-1 to 1⨯10¹² cm^-2eV^-1, the transfer characteristics shift rightward and V_T changes from -0.38 V to -0.22 V. As the location of the peak concentration (E_mid) changes from conduction band edge (E_mid= 3.3 eV) to middle of the bandgap (E_mid =1.7eV), the V_T increases -0.17 V to 0.09V. Similarly, as the number of GBs increases in the channel, the V_T increases and SS degrades as shown in Fig. 6.