A new stable current-sourcing transistor is developed using the band-to-band tunneling phenomenon. A heterojunction between thin film WS2 and heavily hole-doped bulk silicon converts a section of the WS2 contacting the silicon into a hole-doped WS2 inside the WS2 channel, and band-to-band tunneling occurs between the electron-doped and hole-doped WS2. The output current is regulated by the tunneling barrier thickness. The thickness depends on the gate bias for device switching, but is less sensitive to the source bias, enabling stable output currents. The minimum line sensitivity is 2.6%, and the temperature coefficient is 1.4×103 ppm/°C. The device can be operated as a current sourcing device with an ultralow output current and power consumption.