The density of states in the gap of the hydrogenated amorphous silicon prepared by DC glow discharge decomposition has been investigated by field effect measurement. The mobility gap, the flat band voltage and current ratio are obtained from the data. Using the percolation theory, the mobility activation energy and the relation between conductivity and field voltage in hopping conduction are obtained. The mobility gap of the undoped a-Si:H film prepared at 300℃ is 1.7 eV, while the conductivity activation energy is 0.74 eV. The density of states in the gap of the sample at the Fermi level is about $10^{17}(eV^{-1}cm^{-3})$ and flat approaching to $E_F+0.15 eV$ but monotonously increases approaching to the mobility edge.
