Based on the model of thin-film transistors in which the active layer is treated as two-dimensional, the effects of traps are studied. It is shown that when abundant discrete trap states are present, the field-effect mobility becomes temperature dependent. In case the traps are distributed exponentially in energy, a Meyer–Neldel rule for the temperature dependence of mobility and current results. When also the mobile states are distributed in energy, in the so-called band-tail states, the mobility is no longer thermally activated.