In order to obtain stable thin-film silicon devices we are conducting research on the implementation of hot-wire CVD amorphous and polycrystalline silicon in thin-film transistors, TFFs. We present results on TFTs with a profiled active layer (deposited at ≥9 Å/s), and correlate the electrical properties with the structure of the silicon matrix at the insulator/semiconductor interface, as determined with cross-sectional transmission electron microscopy. Devices prepared with an appropriate H2 dilution of SiH4 show cone-shaped crystalline inclusions. These crystals start at the interface in some cases, and in others exhibit an 80nm incubation layer prior to nucleation. The crystals in the TFTs with the incubation layer are not cone-shaped, but are rounded off. The hot-wire CVD deposited devices exhibit a high fieldeffect mobility up to 1.5 cm2V−1s−l. Also, these devices have superior stability upon continuous gate bias stress, as compared to conventional glow-discharge α-Si:H TFTs. We ascribe this to a combination of enhanced structural order of the silicon and a low hydrogen content.