A thin-film semiconductor device includes: a substrate; a gate electrode above the substrate; a gate insulation film above the gate electrode; a channel layer above the gate insulation film, the channel layer having a raised part; a channel protection layer over the raised part of the channel layer, the channel protection layer comprising an organic material, and the organic material including silicon, oxygen, and carbon; an interface layer at an interface between a top surface of the raised part of the channel layer and the channel protection layer, and comprises at least carbon and silicon that derive from the organic material; and a source electrode and a drain electrode each provided over a top surface and a side surface the channel protection layer, a side surface of the interface layer, a side surface of the raised part of the channel layer, and a top surface of the channel layer.