The effect of microvoids on optical properties of a-Si:H deposited by PECVD of SiH4 has been investigated in the deposition temperature range between 143°C and 266°C. Microvoids seem not to affect the density up to H concentrations C
of 15%. The density is decreased only by H incorporation, which, at the same time, influences directly the optical energy gap Eg Above CH=15%, microvoids can easily accommodate H and no further variation either of Eg or the index of refraction n can be appreciated. Microvoids are proven to be affected not only by deposition temperature, but also by deposition time and by a further annealing step, even if at a relative extent.