A thin film transistor is disclosed, which comprises a gate electrode, a gate insulating layer, a semiconductor layer, a source electrode, and a drain electrode, which are disposed on a predetermined substrate, and which is so constructed that the semiconductor layer doesn't exist in any regions, to which strong electric field parallel to said substrate is applied. Besides this thin film transistor a liquid crystal display device using it is disclosed. The thin film transistor according to the present invention has a small increase in the off level current due to photo-current and it is suitable for driving pixels in the liquid crystal display device.