In recent decades, conductive polymer composites (CPCs) have been studied extensively as sensors towards various external stimuli, such as thermal field, stress, organic liquid and vapors, etc. In terms of the thermal sensing behaviors, the CPCs usually exhibit a positive temperature coefficient (PTC) effect, which refers to an increase in resistance upon heating. Most of the improvements in CPC based temperature sensor have been focused on the PTC intensity. However, the negative temperature coefficient (NTC) effect, which is the gradual decline in resistance with rising temperature, is also desired in some occasions. For instance, when CPCs used as smart switching materials for detecting over-temperature danger, the material with such a feature could produce an overcurrent to sound the warning system when the temperature is above the safety range. Unfortunately, to date, the NTC effect tuning of semi-crystalline polymer based CPC is still a challenge. In this work, graphene/ultrahigh molecular weight polyethylene (UHMWPE)/polyamide 6 (PA6) composites were prepared using a solvent co-coagulation method. The graphene was selectively localized in PA6 phase and graphene/PA6 formed continuous conductive layers between UHMWPE particles, generating a novel segregated and double-percolated conductive network. A novel NTC effect of resistivity, which occurs principally above the melting point of polymer matrix, was achieved during the whole heating process. This is evidently different from the common PTC effect of other CPCs. The underlying mechanism originates from the evolutions of the crumpled morphology and the conductivity change of graphene with the increasing temperature. A nice sensing reproducibility and good mechanical property have also been achieved, which is ascribed to the design of the novel segregated microstructure. This work is of significance for the microstructure-properties tuning of CPC based thermal sensing material.