| abstract |
The present invention provides a semiconductor device having stable electrical properties. The present invention also provides a semiconductor device having high reliability. This semiconductor device has a gate electrode, a source electrode, a drain electrode, an oxide semiconductor having a channel formation region, and a gate insulator. The gate insulator has a first layer contacting the channel formation region and a second layer on the first layer, wherein the second layer is a metal oxide, and the metal oxide has a root mean square (RMS) surface roughness of 0.4 nm or less in a measurement range of 1000 nm x 1000 nm. |