Semiconductor device and process for production thereof

A semiconductor device comprising a substrate, and a thin film transistor and a capacitor element disposed on the substrate, wherein

• the thin film transistor includes:
• an island-like oxide semiconductor layer having a channel region, and a first contact region and a second contact region positioned on respective sides of the channel region;
• a gate line disposed so as to overlap at least the channel region of the oxide semiconductor layer;
• a gate insulating layer formed between the gate line and the oxide semiconductor layer;
• a source line electrically connected to the first contact region;
• and
• a drain line electrically connected to the second contact region, the capacitor element includes:
• a first electrode formed from the same conductive film as the gate line;
• a second electrode formed from the same conductive film as the source line;
• and
• a dielectric layer positioned between the first and second electrodes,
• the gate insulating layer has a layered structure including a first insulating film containing an oxide which is in contact with the oxide semiconductor layer, and a second insulating film disposed on the side closer to the gate electrode than the first insulating film, the second insulating film having a dielectric constant higher than the first insulating film, and
• the dielectric layer includes the second insulating film, but does not include the first insulating film.