PURPOSE: To prevent the disconnection of a step-diffenence part in a post- process, by facilitating the flattening of a gate electrode, even in the case of a large screen TFT array.

CONSTITUTION: When a gate electrode 2 of a thin film transistor array of a liquid crystal display is formed below a semiconductor layer 5, a substrate is dipped in solution wherein hydrosilicofluoric acid is supersaturated by SinO2, while gate-patterned resist is left, before a gate insulating layer 4 is formed, and SiO2 is dgposited on the substrate by using boric acid or Al. After that, the post-process of a TFT is perfomed by using the substrate wherein the resist is exfoliated, a gate insulator layer 4, a semiconductor layer 5, and a protective insulator layer 6 are formed, and an extrinsic semiconductor layer 7, a picture element electrode 8, and a source-drain electrode 9 are formed.