The structural and electronic properties of undoped microcrystalline silicon (muc-Si:H) thin films prepared by hot-wire chemical vapor deposition (HWCVD) at various hydrogen dilutions have been studied. UV-visible ellipsometry was used to quantify the crystalline, amorphous and void fractions, and to determine the presence, or otherwise, of an amorphous incubation layer. Diffusion-induced time-resolved microwave conductivity measurements showed that the electronic transport along the growth direction is notably improved for samples prepared by a double-dilution process, where the H, dilution is decreased as a function of the deposition time. These results should be useful for further HWCVD muc-Si:H solar cells. (C) 2001 Published by Elsevier Science B.V. All rights reserved.