Layered materials separated from each bulk crystal can be assembled to form a strain-free heterostructure by using the van der Waals interaction. We demonstrated a heterostructure n-channel depletion-mode β-Ga2O3 junction field-effect transistor (JFET) through van der Waals bonding with an exfoliated p-WSe2 flake. Typical diode characteristics with a high rectifying ratio of ∼105 were observed in a p-WSe2/n-Ga2O3 heterostructure diode, where WSe2 and β-Ga2O3 were obtained by mechanically exfoliating each crystal. Layered JFETs exhibited an excellent I DS–V DS output as well as I DS–V GS transfer characteristics with a high on/off ratio (∼108) and low subthreshold swing (133 mV/dec). Saturated output currents were observed with a threshold voltage of −5.1 V and a three-terminal breakdown voltage of +144 V. Electrical performances of the fabricated heterostructure JFET were maintained at elevated temperatures with outstanding air stability. Our WSe2–Ga2O3 heterostructure JFET paves the way to the low-dimensional high-power devices, enabling miniaturization of the integrated power electronic systems.