Abstract In this paper, a novel N-channel Tunnel Field Effect Transistor (TFET) i.e., Trigate Silicon-ON-Insulator (SOI) N-TFET with high-k spacer is proposed for better Sub-threshold swing (SS) and OFF-state current (I OFF ) by keeping in mind the sensitivity towards temperature. The proposed model can achieve a Sub-threshold swing less than 35 mV/decade at various temperatures, which is desirable for designing low power CTFET for digital circuit applications. In N-TFET source doping has a significant effect on the ON-state current (I ON ) level; therefore more electrons will tunnel from source to channel region. High-k Spacer i.e., HfO 2 is used to enhance the device performance and also it avoids overlapping of transistors in an integrated circuits (IC’s). We have designed a reliable device by performing the temperature analysis on Transfer characteristics, Drain characteristics and also on various performance metrics like ON-state current (I ON ), OFF-state current (I OFF ), I ON /I OFF , Trans -conductance (g m ), Trans -conductance Generation Factor (TGF), Sub-threshold Swing (SS) to observe the applications towards harsh temperature environment.