There are provided a TFT, a TFT substrate using the TFT, a method of fabricating the TFT substrate, and an LCD. The TFT includes a source region, a drain region, and a gate electrode having an opening. The opening of the gate electrode is to enhance the light sensing ability of the TFT when it is used as a light sensor, since light is incident into a region where the opening is formed. The TFT including the gate having the opening can be used in a substrate of a flat display or an LCD using such a substrate. The above TFT can sense light incident from outside the display to adjust the brightness of the screen according to the external illumination.