A method of manufacturing an array substrate for a liquid crystal display device includes forming a gate line, a gate pad, a gate electrode, and a data pad on a substrate through a first mask process, forming a gate insulating layer on a substantial part of an entire surface of the substrate including the gate line, the gate pad, the gate electrode, and the data pad, forming a data line, a source-drain pattern and an active layer on the gate insulating layer and forming a gate pad contact hole and a data pad contact hole in the gate insulating layer through a second mask process, and forming a pixel electrode, a gate pad terminal, a data pad terminal, a source electrode, a drain electrode, and an ohmic contact layer through a third mask process.