A self-aligned LDD TFT and a fabrication method thereof. The method includes providing a semiconductor layer. A first masking layer is provided over a first region of the semiconductor layer, said first masking layer comprising a material that provide a permeable barrier to a dopant. The semiconductor layer is exposed, including the first region covered by the first masking layer, to the dopant, wherein the first region covered by the first masking layer is lightly doped with the dopant in comparison to a second region not covered by the first masking layer.