Cubic silicon carbide (3C-SiC) on silicon (Si) is an excellent platform for developing sensors that can function in a harsh environment due to its superior mechanical, electrical, chemical, optoelectronic properties and low wafer cost. Here, we report a position-sensitive detector (PSD) based on the heterojunction formed between n-type SiC and p-type Si. The PSD utilizes the lateral photovoltaic effect (LPE) with a linear dependence of LPE on laser spot positions. The position sensitivity is found to be 554.82 mV/mm at zero bias conditions under an illumination of 200 μW (637 nm), which is among the most sensitive LPE-based PSDs to date. The generation of the lateral photovoltage (LPV) under light illumination is investigated by examining the band diagram of the 3C-SiC/Si heterojunction. The influence of the illumination intensity and wavelength on the position sensitivity is also explained. This work demonstrates a potential application for ultrasensitive, self-powered optoelectronic sensing of the n-3C-SiC/p-Si platform.