The thermal properties of the phase-change chalcogenide alloy Ge2Sb2Te5 in its three phases (amorphous, cubic, and hexagonal) and of Si3N4 and SiO2 have been studied to obtain reliable values for device modeling. Thermal conductivity was determined, along with a quantitative estimation of the thermal resistances of the layers’ interfaces, not negligible for highly scaled devices. Electrical resistivity of the chalcogenide material has also been investigated during the phase transition by in situ measurement at constant heating rate.