Volcanic arcs such as the Barisan Mountains have been identified as attractive areas for the utilization of geothermal energy, as exemplified by Ulubelu in Lampung and Sarulla in North Sumatra. However, environmental factors in the Barisan Mountains remain a primary obstacle to the exploration and exploitation of geothermal energy. The back-arc basins of Sumatra exhibit the highest heat flow worldwide; however, the heat source in this area remains a controversial issue. This study aims to investigate the origin of the high heat flow in the back-arc basins of Sumatra (North, Central, and South Sumatra basins) based on geothermal data from 384 oil wells and the current literature for geological evaluation. The findings of this study indicate that the back-arc basins of Sumatra experienced severe extensional deformation during the Tertiary Period through a large pull-apart and slab rollback mechanism. This deformation resulted in the thinning of the continental crust in this region (27–32 km) and the formation of multiple normal faults. Consequently, the presence of magma resulting from mantle upwelling implies a high heat flow in the back-arc basins of Sumatra. This condition ranks the back-arc basins of Sumatra among the highest heat flow regions of the world, with heat flows >100 mW/m2. These findings indicate that the back-arc basins of Sumatra have significant opportunities to exploit their geothermal energy potential. This study provides novel insights into the potential of geothermal energy, particularly in the back-arc basins of Sumatra.