The convergence of the Internet of Things (IoT) and 5G technology is creating a high demand in sensor signals, prompting a shift toward self-powered sensors as eco-friendly alternatives to the conventional battery-powered ones. The 3C-SiC/Si heterostructure recently has gained significant attention for sensing applications, including self-powered sensors. However, it has remained unclear about the sensing properties and the underlying physics of the sensing mechanism of the unintentionally doped n-SiC/p-Si heterostructure, hindering the design optimization of SiC/Si heterojunction self-powered devices for diverse applications. This study investigates the thermo-phototronic effect and its underlying mechanism in an unintentionally doped n-3C-SiC/p-Si heterostructure for self-powered sensors. The sensors can be self-powered by absorbing energy from photons to generate photovoltage and photocurrent as high as 110 mV and 0.8 μA. In addition, widening the electrode spacing increased the photovoltage of the device by as much as 122% and the photocurrent by as much as 65%. When the temperature gradient is progressively increased by heating one electrode, the photovoltage decreases gradually, while the current exhibits an initial increase of up to 10%, followed by a decline. These tunable characteristics are attributed to the capability of the heterostructure to control the transport of charge carriers and the impact of unintentionally doped n-SiC on the diffusion of charge carriers. The results of this study can be applied in the development of photodetectors, thermal sensors, and position detectors with tunable sensing performance.