A three mask process for forming an LCD substrate includes, depositing in sequence on a base substrate a gate metallic layer, a gate insulation layer and a channel layer. A first photoresist pattern is used to form a gate electrode of a switching device, a channel pattern and a gate line on the gate electrode. A transparent conductive layer and a source metallic layer are deposited in sequence on the base substrate having the channel pattern. A source electrode and a drain electrode of the switching device, a pixel electrode and a source line electronically connected to the drain electrode, are formed by a second photoresist pattern. A first protective insulation layer is formed, and the first protective insulation layer on the pixel electrode is removed by a third photoresist pattern. Therefore, by the three masks process yields a simplified manufacturing process in which the lower portion of the source metallic pattern is not formed and display quality is improved.