In a display device of the present invention which forms thin film transistors on a substrate, the thin film transistor comprises: a silicon nitride film which is formed on the substrate in a state that the silicon nitride film covers a gate electrode; a silicon oxide film which is selectively formed on the silicon nitride film; a semiconductor layer which is formed at least on an upper surface of the silicon oxide film and includes a pseudo single crystal layer or a polycrystalline layer; and a drain electrode and a source electrode which are formed on an upper surface of the semiconductor layer by way of a contact layer, wherein either one of the pseudo single crystal layer and the poly-crystalline layer is formed by crystallizing the amorphous silicon layer, and a peripheral-side wall surface of the pseudo single crystal layer or the polycrystalline layer is contiguously constituted with a peripheral-side wall surface of the silicon oxide film below the pseudo single crystal layer or the polycrystalline layer without a stepped portion.