Buckypaper thermal interface materials (TIMs) with various heat treated (1100 °C, 1500 °C and 3000 °C) carbon nanofibers (CNFs) were explored. A transient spike power system was designed with hot and cold plate method where these TIMs were subjected to two conditions: uniform heat pulse of 24 W and power spikes of 24–96 W under transient loads. The parametric study showed significant decrement in the thermal resistance in conjunction with the increasing heat-treatment temperature of CNF. This was achieved due to high thermal conductivity and crytallinity of CNFs at high temperatures. The overall results reveal that the TIM with high heat treated (HHT) CNF is more temperature resistant than dry contact with more than 50% increase in the heat transport across it.