Position-sensitive detector (PSD) is a popular type of noncontact optical position sensor that has important roles in various applications. Cubic-silicon carbide on silicon (3C-SiC/Si) is a promising platform to develop optoelectronic sensors for harsh environment applications thanks to the superior robustness of the SiC, the low wafer cost, and the high compatibility with the well-established Si micro/nano fabrication technology. Here, we report an enhanced lateral photovoltaic effect (LPE) in 3C-SiC/Si heterojunction under an external electric field, and demonstrate the effect in an ultrasensitive PSD. We observed a position sensitivity of 1550 mV/mm, which is a five-time increase compared to the case without electric field. The generation and transport of the photo-induced charge carriers are investigated by examining the band diagram of the 3C-SiC/Si heterojunction to provide a detail explanation of the phenomenon. Our findings in this work demonstrate the potential of the 3C-SiC/Si heterojunction to develop high-performance noncontact optical sensors for harsh environment applications.