Herein we report a light harvesting self-powered strain sensor using a monolithic heterojunction structure. Firstly, a strain sensor in a geometry of a cantilever with a 3C-SiC/Si heterojunction sensing element is fabricated. Secondly, light energy harvesting ability of the strain sensor is demonstrated under illumination of a commercial LED. Finally, the performance of the sensor under the self-powered mode is evaluated by inducing strain in the sensing element and simultaneously monitoring the change of converted electrical energy. Under illumination of LED with light power of 428 μW, the generated photovoltage is as high as approximately 16.4 mV. The sensor can harvest light energy convert it into electrical energy to power itself and sense the strain ranging from 200 ppm to 700 ppm with a sensitivity of approximately 0.06 μV /ppm.