The incorporation of multiphysics stimuli with traditional sensing effects results in an approach for increasing the sensitivity of mechanical sensors, in particular strain sensing. This paper reports on the giant piezotronic effect in a p-GaN/AlGaN/GaN heterojunction coupled with UV illumination and tuning current that can reach a strain sensitivity of as high as 70680. In comparison to an identical configuration without coupling, this value represents a 100-fold improvement. This sensitivity is one of the greatest for the piezotronic effect in semiconductors that have been documented to date. The intensification of the piezotronic effect in the p-GaN/AlGaN/GaN heterojunctions was ascribed to the formation of a carrier concentration gradient in the AlGaN and GaN layers under UV illumination coupled with the potential-balancing effect by a tuning current. In addition, the result showed a significant improvement in repeatability, stability, and detectable range of the strain sensor utilizing this phenomenon. The ultrahigh sensitivity strain sensing technique will open the way for the establishment of mechanical sensors that are tremendously sensitive, trustworthy, and efficient.