A method for forming a liquid crystal display device includes incremental removal of a gate insulator. After forming a gate line layer, a gate insulator, a semiconductor layer, a data layer and a photoresist layer, a mask is used to define a plurality of regions in the photoresist layer through selective development. The developed portions of the photoresist layer are removed and parts of the underlying layers are etched in a plurality of steps using the photoresist layer as a mask. The gate insulator is partially removed during the etching of the data layer and completely removed during formation of source and drain electrodes.