We report an alumina-encapsulated microcircuit on a diamond anvil for high-pressure and high-temperature electrical conductivity measurement. An alumina thin film was deposited on a diamond anvil as a thermal insulation layer for laser heating, on which a molybdenum film was deposited and photolithographically fabricated to a van der Pauw circuit. The introduction of the alumina layer significantly improves the laser heating performance. This specially fabricated diamond anvil permits us to measure the resistivity of (Mg0.875 Fe0.125) 2 Si O4 at 3450 K and 35 GPa in a laser-heated diamond anvil cell. We expect to substantially extend the pressure-temperature scale of in situ resistivity measurement.