A high optoelectronic performance ReS₂/ReSe₂ van der Waals (vdW) heterojunction phototransistor utilizing thin hafnium oxide (HfO₂) as a local-back-gate dielectric layer was prepared and studied. The heterojunction-based phototransistor exhibits a superior electrical performance with a large rectification ratio of ∼10³. Furthermore, unlike diode-like heterojunction devices, the innovative introduction of a local-back-gate in this phototransistor provides an outstanding gate-tunable capability with an ultra-low off-state current of 433 fA and a high on/off current ratio of over 10⁶. And under optical excitation of a wide spectrum from 400 to 633 nm, an excellent photodetection responsivity at the 10⁴ A W⁻¹ level and the maximum normalized detectivity of 1.8 × 10¹⁵ Jones @ 633 nm have been demonstrated. Such high performances are attributed to the band alignment of the type-II heterojunction and the suppression of dark current by the local-back-gate. This work provides a promising reference for two-dimensional (2D) Re-based heterojunction optoelectronic devices.