Semiconductor Device and Memory Device

A semiconductor device comprising:

• a source electrode and a drain electrode of a transistor over a first insulator;
• an oxide semiconductor of the transistor over the first insulator;
• a second insulator over the source electrode and the drain electrode and comprising an opening between the source electrode and the drain electrode;
• a third insulator over and in contact with the second insulator;
• and
• a fourth insulator over and in contact with the third insulator,
• wherein the oxide semiconductor is positioned inside the opening of the second insulator, and
• wherein the first insulator and the fourth insulator are in contact with each other in a region where the second insulator and the third insulator do not exist.