The effects of dangling bonds on the dark conductivities of undoped a-Si:H have been studied by computer model calculation of Fermi level, in which Fermi level was determined by charge neutrality with considering dangling bonds and density of states. With more than $10^{16}/cm^3$ dangling bonds, the temperature shift of Fermi level was less than $1.0\times10^{-4}$eV/K, so above effect on the conductivity prefactor was less than factor 3. Therefore, if the temperature shift of mobility edge(Ec) is cosidered, conductivity prefactor of light soaked state could almost be true value, and its value was between $1.1\times10^4$ S/cm and $3.1\times10^4$S/cm. To fit the conductivities of annealed and light soaked state with reasonable dangling bond density, their energy level should be about 1.02eV and 1.09eV below Ec, respectively. On the other hand, it is found that impurities (less than $10^{14}/cm^3$) could change Fermi level of annealed state.
