A heterogeneous charge transport model for microcrystalline silicon based on fluctuation-induced tunneling is presented that fits the low-temperature saturation observed in dark conductivity measurements and accounts for the film microstructure. Excellent agreement is found when the model is applied to data reported in the literature, particularly for highly crystalline samples, which produce the highest performance transistors. Values obtained for the three fitting parameters are consistent with typical measurements of microcrystalline silicon film morphology and the conduction band offset between amorphous and crystalline silicons.