A thin-film transistor device includes: a gate electrode above a substrate; a gate insulating film on the gate electrode; a crystalline silicon thin film above the gate insulating film; a first semiconductor film above the crystalline silicon thin film; a pair of second semiconductor films above the first semiconductor film; a source electrode over one of the second semiconductor films; and a drain electrode over an other one of the second semiconductor films. The first semiconductor film is provided on the crystalline silicon thin film. A relationship ECP