Black phosphorous (BP), an excellent two-dimensional (2D) monoelemental layered p-type semiconductor material with high carrier mobility and thickness-dependent tunable direct bandgap structure, has been widely applied in various devices. As the essential building blocks for modern electronic and optoelectronic devices, high quality PN junctions based on semiconductors have attracted widespread attention. Herein, we report a junction field-effect transistor (JFET) by integrating narrow-gap p-type BP and ultra-wide gap n-type β-Ga₂O₃ nanoflakes for the first time. BP and β-Ga₂O₃ form a vertical van der Waals (vdW) heterostructure by mechanically exfoliated method. The BP/β-Ga₂O₃ vdW heterostructure exhibits remarkable PN diode rectifying characteristics with a high rectifying ratio about 10⁷ and a low reverse current around pA. More interestingly, by using the BP as the gate and β-Ga₂O₃ as the channel, the BP/β-Ga₂O₃ JFET devices demonstrate excellent n-channel JFET characteristics with the on/off ratio as high as 10⁷, gate leakage current around as low as pA, maximum transconductance (g_m) up to 25.3 µS and saturation drain current (I_DSS) of 16.5 µA/µm. Moreover, it has a pinch-off voltage of –20 V and a minimum subthreshold swing of 260 mV/dec. These excellent n-channel JFET characteristics will expand the application of BP in future nanoelectronic devices.