Polymer thin-film transistors based on poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) have been studied in the
temperature range from 130 to 300K. In this temperature range both the field effect mobility and the drain current show
thermally activated behaviour. The channel current at low gate voltage ( |Vgs|<|Vth| ) can be fitted with a power
function of gate voltage. We deduce the presence of an exponential distribution of localized states above the dominant
transport level from the gate bias and temperature dependence of the drain current.