The spacer design of the negative-capacitance FinFET (NC-FinFET) is investigated by using Sentaurus technology computer-aided design (TCAD). The spacer affects not only the gate capacitance but also the drain current due to the additional gate control from the outer fringing field. It is found that in a heavily loaded circuit although the fin corner spacer improves the inverter propagation delay of the baseline FinFET, the NC-FinFET requires the fin selective spacer with the spacer height up to the ferroelectric thickness for better capacitance matching. When the wire capacitance is 3 times larger than the gate capacitance, the inverter propagation delay of the NC-FinFET with the fin selective spacer can be improved by 8% against the full spacer design. However, with the consideration of process complexity, the air spacer may still be attractive in the NC-FinFET, since it does not suffer from the amplified gate capacitance. © 1980-2012 IEEE.