This paper shows a wide range of applications of the hot-wire chemical vapor deposition (HWCVD) method to either deposit photosensitive hydrogenated amorphous silicon (a-Si:H), polysilicon (poly-Si) and heterogeneous Si materials, dielectric hydrogenated amorphous silicon nitride (a-SiNx:H) of device quality, or to carry out hydrogen passivation treatments. Various choices of deposition parameters, i.e. process temperature, wire temperature and filament materials, have been investigated to decide the growth rate, substrate material and device configuration. The main feature of our poly-Si films is the compact nature, which manifests itself in anti-ferromagnetically-coupled defect dimer formation and hydrogen diffusion through compact sites. Very thin grain-boundary defects, purely intrinsic nature and very low oxygen incorporation, both during and post-deposition, have resulted in poly-Si films of device quality. Thin film transistors (TFTs) and solar cells have been fabricated using the above-mentioned HWCVD-deposited materials. Highly stable TFTs in the inverted staggered configuration, using heterogeneous Si, showed a field effect mobility of 1.5 cm2 V−1 s−1, whereas top-gate TFTs using poly-Si on glass showed a mobility of 4.7 cm2 V−1 s−1. The paper demonstrates the application of HWCVD a-SiNx as a dielectric material in bottom-gate TFTs, and complete TFTs have been successfully fabricated by the HWCVD process (except the contact layers). Solar cells in an n–i–p structure on plain stainless steel (SS) substrate showed efficiencies of 7.2% for a-Si:H and 4.4% for poly-Si i-layers. An a-Si/poly–Si tandem cell, with all-HWCVD i-layers, on a SS substrate without a back reflector and texturization yielded an efficiency of 8.1%. This was achieved at a deposition rate of 10 Å s−1 for poly-Si.