2D materials have shown great promise for next‐generation high‐performance photodetectors. However, the performance of photodetectors based on 2D materials is generally limited by the tradeoff between photoresponsivity and photodetectivity. Here, a novel junction field‐effect transistor (JFET) photodetector consisting of a PdSe₂ gate and MoS₂ channel is constructed to realize high responsivity and high detectivity through effective modulation of top junction gate and back gate. The JFET exhibits high carrier mobility of 213 cm² V⁻¹ s⁻¹. What is more, the high responsivity of 6 × 10² A W⁻¹, as well as the high detectivity of 10¹¹ Jones, are achieved simultaneously through the dual‐gate modulation. The high performance is attributed to the modulation of the depletion region by the dual‐gate, which can effectively suppress the dark current and enhance the photocurrent, thereby realizing high detectivity and responsivity. The JFET photodetector provides a new approach to realize photodetectors with high responsivity and detectivity.