The authors demonstrate the possibility of using self-bias voltage on the radio-frequency electrode of a capacitively coupled deposition system as a diagnostic tool to detect the amorphous-to-microcrystalline silicon transition during the exposure of a-Si:H thin films to a hydrogen plasma. This is achieved by combining self-bias voltage (V-dc) and kinetic-ellipsometry measurements, which provide real-time information on the film properties. On intrinsic and n-type a-Si:H films, the hydrogen-plasma exposure results in the formation of a hydrogen-modified layer, which is accompanied with a decrease in the absolute values of V-dc, until a plateau corresponding to the nucleation and the growth of the microcrystalline layer occurs. On p-type a-Si: H, the amorphous-to-microcrystalline transition is characterized by a rapid increase in the absolute values of V-dc. This particular trend is ascribed to the effects of boron on both the solid and plasma phases. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3305719]