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Abstract While monazite (LaPO₄) does not flash sinter even at high fields of 1130 V/cm and temperatures of 1450°C, composite systems of 8YSZ–LaPO₄and Al₂O₃–LaPO₄have been found to more readily flash sinter. 8YSZ added to LaPO₄greatly lowered the furnace temperature for flash to 1100°C using a field of only 250 V/cm. In these experiments,‐Al₂O₃alone also did not flash sinter at 1450°C even with high fields of 1130 V/cm, but composites of Al₂O₃–LaPO₄powders flash sintered at 900‐1080 V/cm at 1450°C. Alumina–monazite (Al₂O₃–LaPO₄) composites with compositions ranging from 25 vol% to 75 vol% Al₂O₃were flash sintered with current limits from 2 to 25 mA/mm². Microstructures were evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A eutectic microstructure was observed to form in all flash sintered Al₂O₃–LaPO₄composites. With higher power (higher current limits), eutectic structures with regular lamellar regions were found to coexist in the channeled region (where both the current and the temperature were the highest) with large hexagonal‐shaped‐Al₂O₃grains (up to 75 m) and large irregular LaPO₄grains. With lower power (lower current limits), an irregular eutectic microstructure was dominant, and there was minimal abnormal grain growth. These results indicate that Al₂O₃–LaPO₄is a eutectic‐forming system and the eutectic temperature was reached locally during flash sintering in regions. These eutectic microstructures with lamellar dimensions on the scale of 100 nm offer potential for improved mechanical properties.