The electronic transport properties of a series of samples prepared by hot-wire chemical vapor deposition with a transition from a-Si:H to μc-Si:H were measured applying the photoconductive frequency mixing technique. We found both improved stability against light-soaking and different values for the photomixing electron lifetime and mobility close to the onset of microcrystallinity as compared to the amorphous state. In particular, the mobility-lifetime product of charge carriers in some of the μc-Si:H samples turns out to lie about two orders of magnitude higher than that of a-Si:H films. The mobility on the other hand, is shown rather to decrease in the transition to the μc-region. Additional measurements of the range and the depth of long range potential fluctuations yield a possible explanation for our results in that grain boundaries may serve as scattering centers and barriers against recombination.