Position-sensitive detectors (PSDs) utilising the lateral photovoltaic effect (LPE) are actively being explored to achieve precise optical alignments for applications such as surface profiling, motion tracking, and robotics. However, the development of ultrasensitive PSDs has faced great challenges due to the limitation of conventional architectures and nature of photosensitive materials. Herein, we propose a novel PSD nanoarchitecture based on horizontally-aligned double 3C-SiC/Si heterostructures. The unique device configuration allows the effective generation, separation, and migration of photogenerated carriers to one electrode, while eliminating the diffusion of these charge carriers to the other, enabling a large gradient of charge or lateral photovoltage between the electrodes. The PSD showed an ultra-high sensitivity of 1780 mV/mm at an illumination intensity of 5.6 W/cm2 (980 nm) at zero bias conditions (i.e., self-powered), which is approximately 620% more sensitive than that of standard-type 3C-SiC/Si PSD and over 250% larger than the best position-sensitivity detector reported to date. The innovative nanoarchitecture demonstrated in this work holds promises for developing industry-compatible ultra-sensitive self-powered position-sensitive detectors.