The density of states （DOS） above Fermi level of hydrogenated microcrystalline silicon （μc-Si:H） films is correlated to the material microstructure. We use Raman scattering and infrared absorption spectra to characterize the structure of the films made with different hydrogen dilution ratios. The DOS of the films is examined by modulated photocurrent measurement. The results have been accounted for in the framework of a three-phase model comprised of amorphous and crystalline components， with the grain boundary as the third phase. We observed that the DOS increases monotonically as the grain boundary volume fractions fgb is increased， which indicates a positive correlation between the DOS and the grain boundary volume fraction.