We have developed heat resistive vibrational energy harvester using silicon oxide electret. The electret in this work is known to be structurally robust owing to the five-coordinated silicon atoms in the silicon oxide molecular network. We utilize a vacuum package to suppress the degradation of electret potential at an elevated temperature of 100 ˚C, making it possible to produce robust energy harvesters that could be used on high-temperature equipment in factories and plants where continuous monitoring is needed using IoT type sensors.