An array substrate for a liquid crystal display device includes: a gate line and a gate electrode on a substrate, the gate electrode connected to the gate line; a gate insulating layer on the gate line and the gate electrode, the gate insulating layer including an organic insulating material such that a radical of carbon chain has a composition ratio of about 8% to about 11% by weight; a semiconductor layer on the gate insulating layer over the gate electrode; a data line crossing the gate line to define a pixel region; source and drain electrodes on the semiconductor layer, the source electrode connected to the data line and the drain electrode spaced apart from the source electrode; a passivation layer on the data line, the source electrode and the drain electrode, the passivation layer having a drain contact hole exposing the drain electrode; and a pixel electrode on the passivation layer, the pixel electrode connected to the drain electrode through the drain contact hole.