A thin film transistor comprising: an active layer on a substrate; a gate electrode disposed apart from the active layer to at least partially overlap the active layer; and a gate insulation layer between the active layer and the gate electrode, wherein the gate insulation layer covers a whole top surface of the active layer facing the gate electrode except a contact hole region or a region, contacting a conductive element, of the active layer, the active layer comprises: a channel part overlapping the gate electrode; a conductivity-providing part (133a; 133b) which does not overlap the gate electrode; and an offset part (132a; 132b) between the channel part and the conductivity-providing part (133a; 133b), the offset part (132a; 132b) does not overlap the gate electrode, and the conductivity-providing part (133a; 133b) is doped with a dopant, characterized in that: when a width of the channel part is L1 and a width of the offset part (132a; 132b) is L2, the thin film transistor satisfies Equation 1 below, L1 × L2 × 1/ η 1 ≥ 1, where the widths L1 and L2 are measured along the current direction in the channel, and η1 satisfies a relationship 0.5 μm 2 ≤ η1 ≤ 1.5 μm 2. an active layer on a substrate; a gate electrode disposed apart from the active layer to at least partially overlap the active layer; and a gate insulation layer between the active layer and the gate electrode, wherein the gate insulation layer covers a whole top surface of the active layer facing the gate electrode except a contact hole region or a region, contacting a conductive element, of the active layer, the active layer comprises: a channel part overlapping the gate electrode; a conductivity-providing part (133a; 133b) which does not overlap the gate electrode; and an offset part (132a; 132b) between the channel part and the conductivity-providing part (133a; 133b), the offset part (132a; 132b) does not overlap the gate electrode, and the conductivity-providing part (133a; 133b) is doped with a dopant, characterized in that: when a width of the channel part is L1 and a width of the offset part (132a; 132b) is L2, the thin film transistor satisfies Equation 1 below, L1 × L2 × 1/ η 1 ≥ 1, where the widths L1 and L2 are measured along the current direction in the channel, and η1 satisfies a relationship 0.5 μm 2 ≤ η1 ≤ 1.5 μm 2. a channel part overlapping the gate electrode; a conductivity-providing part (133a; 133b) which does not overlap the gate electrode; and an offset part (132a; 132b) between the channel part and the conductivity-providing part (133a; 133b), the offset part (132a; 132b) does not overlap the gate electrode, and the conductivity-providing part (133a; 133b) is doped with a dopant, characterized in that: when a width of the channel part is L1 and a width of the offset part (132a; 132b) is L2, the thin film transistor satisfies Equation 1 below, L1 × L2 × 1/ η 1 ≥ 1, where the widths L1 and L2 are measured along the current direction in the channel, and η1 satisfies a relationship 0.5 μm 2 ≤ η1 ≤ 1.5 μm 2. when a width of the channel part is L1 and a width of the offset part (132a; 132b) is L2, the thin film transistor satisfies Equation 1 below, L1 × L2 × 1/ η 1 ≥ 1, where the widths L1 and L2 are measured along the current direction in the channel, and η1 satisfies a relationship 0.5 μm 2 ≤ η1 ≤ 1.5 μm 2.