A method is provided for controlling the channel length in a thin-film transistor (TFT). The method forms a printed ink first source/drain (S/D) structure overlying a substrate. A fluoropolymer mask is deposited to cover the first S/D structure. A boundary region is formed between the edge of the fluoropolymer mask and the edge of the printed ink first S/D structure, having a width. Then, a primary ink is printed at least partially overlying the boundary region, forming a printed ink second S/D structure, having an edge adjacent to the fluoropolymer mask edge. After removing the fluoropolymer mask, the printed ink first S/D structure edge is left separated from the printed ink second S/D structure edge by a space equal to the boundary region width. A semiconductor channel is formed partially overlying the first and second S/D structures, having a channel length equal to the boundary region width.