A thin film transistor which can be used in an LCD display panel includes an insulator substrate, a gate electrode located on the insulator substrate, an insulator film provided on the insulator substrate and the gate electrode, and a polycrystalline silicon film located on the insulator film. A channel is defined in a first portion of the polycrystalline silicon film over the gate electrode, and a drain and a source are defined in second and third portions of the polycrystalline silicon film over the insulator substrate. Grain sizes of the drain and source are equal to or greater than a grain size of the channel.