Abstract: The invention relates to an improved thin film semiconductor p-n junction device and its method of fabrication, utilizing vacuum deposition techniques, whereby continuous/batch processing may be utilized, capable of mass producing p-n junction devices; e.g. solar cells, with large surface areas and good operating efficiency and at low cost. A novel feature of the proposed device and its method of fabrication is the formation of the bottom electrode of the device, located between the nonconducting substrate and the overlying silicon semiconductor layer, as a metal boride region which possesses several characteristics particularly necessary to the fabrication of thin film silicon solar cells for example, having improved structural and operating properties, as well as good operating efficiency.