We report on the photocurrent response of hydrogenated nanocrystalline silicon (nc-Si:H) thin films under external bias voltages. The band gap transition and internal photoemission photocurrent of the nc-Si:H thin films can be enhanced and controlled by adjusting the depletion and inversion layers in the metal-semiconductor junction through the external bias voltage. The photocurrent response from the internal photoemission is found to be able to extend the photodetection wavelength of the Si material to the optical telecommunication range of 1.3–1.6 μm.