The voltage-current characteristics of a-Si:H films were measured in the sandwitch structure. The gap-state distribution was studied by space-charge-limited current(SCLC) method and the switching was observed. A small peak in the gap-state distribution at E -0.52eV was found. This peak is attributed to dangling bonds. Obtained density of state was $2-4\times10^{16}eV^{-1}cm^{-3}$ near Ec-0.5 eV. Two types of switching were observed in a-Si:H films. These two types of switching were supposed to arise from inhomogeneity of the sample. In the T type of switching, the threshold voltage and $I_{on}$ were independent of temperature and forming process was observed. On the other hand, in S type defined voltage Vx was dependent on temperature. The threshold switching is attributed to avalanche breakdown through the produced defect-rich, altered region in the forming process.
