Abstract: A self-aligned LDD TFT and a fabrication method thereof. A substrate is provided, on which a semiconductor layer is formed. A first masking layer is provided over a first region of the portion of the semiconductor layer. The first masking layer comprises a material that provides a permeable barrier to a dopant. The semiconductor layer including the first region covered by the first masking layer is exposed 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 region.