A structure of a thin film transistor and a method for making the same are provided. The structure includes a strip-shaped silicon island, a gate, and a first and second ion doping regions. The strip-shaped silicon island is a thin film region with a predetermined long side and short side, and farther has a plurality of lateral grain boundaries substantially parallel to the short side of the silicon island. The gate is located over the silicon island and substantially parallel to the lateral grain boundaries. The first and second ion doping regions, used as source/drain regions of the TFT, are located at two sides along the long side of the island and substantially perpendicular to the gate.