Low-dimensional semiconductor p-n junctions as components for optoelectronic devices are considered to be more promising than thin film equivalents. We fabricated heterojunction p-n solar blind photodiodes with the configuration of n-type β-Ga2O3 nanobelts contacted onto p-Si substrates. The junction between β-Ga2O3 and Si was formed by van der Waals interactions. The fabricated heterojunction p-n diodes exhibited typical rectifying current. voltage characteristics, with a rectification ratio as high as 1.56×104 at ±20 V and an ideality factor of approximately eight. Photoresponsive measurements showed that the heterojunction p-n diodes had a high sensitivity and selectivity for light at a wavelength of 254 nm, with fast response and decay characteristics. For the fast-response components, the response time constant was 4.06 s and the decay time constant was 0.16 s. The exfoliated β-Ga2O3 nanobelt/Si p-n heterojunction presented here constitutes a functional unit for low-dimensional ultra-wide bandgap electronic and optoelectronic devices.