The field‐effect conductance activation energyEaas a function of the gate voltageVgis investigated for polycrystalline silicon thin‐film transistors. An analytical expression forEais obtained for various models of the bulk and interface states. Using a computer minimization program to fit the experimentalEavsVgdata with the theory, the energy distribution of the bulk states and the interface states are separated for nonhydrogenated and hydrogenated polycrystalline silicon thin‐film transistors. In both cases, the bulk states have exponential band tails and a wide peak near the midgap and the interface states have an exponential distribution from the band edge.