Method of manufacturing array substrate for use in liquid crystal display device

A method is disclosed for manufacturing an array substrate for use in a display device. The method includes providing a base substrate, forming a gate line on the base substrate using a first mask, forming sequentially a gate insulating layer, a semiconductor layer and a metal layer over the base substrate and the gate line, patterning the metal layer using a second mask to form a data line and a metal portion on the semiconductor layer, forming a protection layer over the data line, the metal portion and the semiconductor layer, forming a photoresist pattern on the protection layer over the data line using a third mask to define a first structure, applying at least two separate etching steps on the first structure to leave the gate insulating layer of a uniform thickness over the gate line and to pattern layers below the photoresist pattern, and forming a pixel electrode over a portion of the gate insulating layer on the gate line using a fourth mask.