IoT devices in a sensor network require a new energy-efficient transistor which operates at ultralow voltage and power employing energy-harvesting techniques. In this paper, we propose a new steep slope transistor by combining the feature of tunnel FET(TFET) and negative capacitance FET(NCFET) which have been independently studied so far. In NCTFET, band-to-band tunneling in TFET can be enhanced by negative capacitance effect of ferroelectric gate insulator. This results in improvement of subthreshold slope. The energy efficiency of NCTFET is about 10 times higher than conventional MOSFET and TFET. Therefore, NCTFET is expected to become a new CMOS platform for IoT application.