Semiconductor device, display device, and electronic appliance

A display device comprising:

• a light emitting element;
• a first transistor;
• a second transistor;
• a third transistor;
• a fourth transistor;
• a capacitor;
• a first wiring;
• a second wiring;
• and
• a third wiring,
• wherein one of a source and a drain of the first transistor is directly connected to a pixel electrode of the light emitting element,
• wherein the other of the source and the drain of the first transistor is directly connected to the first wiring,
• wherein a first electrode of the capacitor is directly connected to a gate of the first transistor,
• wherein a second electrode of the capacitor is directly connected to the one of the source and the drain of the first transistor,
• wherein one of a source and a drain of the second transistor is directly connected to the gate of the first transistor,
• wherein the other of the source and the drain of the second transistor is connected to the second wiring,
• wherein one of a source and a drain of the third transistor is directly connected to the light emitting element,
• wherein the other of the source and the drain of the third transistor is connected to the third wiring,
• wherein one of a source and a drain of the fourth transistor is directly connected to the gate of the first transistor,
• wherein a gate insulating film is over a semiconductor layer,
• wherein a gate electrode of the first transistor and the first electrode of the capacitor over the gate insulating film,
• wherein an interlayer insulating film is over the gate electrode of the first transistor and the first electrode of the capacitor,
• wherein the second electrode of the capacitor is over the interlayer insulating film,
• wherein the first electrode of the capacitor overlaps the semiconductor layer, and
• wherein the second electrode of the capacitor is in contact with the semiconductor layer.

A display device comprising:

• a light emitting element;
• a first transistor;
• a second transistor;
• a third transistor;
• a fourth transistor;
• a capacitor;
• a first wiring;
• a second wiring;
• and
• a third wiring,
• wherein one of a source and a drain of the first transistor is directly connected to a pixel electrode of the light emitting element,
• wherein the other of the source and the drain of the first transistor is directly connected to the first wiring,
• wherein a first electrode of the capacitor is directly connected to a gate of the first transistor,
• wherein a second electrode of the capacitor is directly connected to the one of the source and the drain of the first transistor,
• wherein one of a source and a drain of the second transistor is directly connected to the gate of the first transistor,
• wherein the other of the source and the drain of the second transistor is connected to the second wiring,
• wherein one of a source and a drain of the third transistor is directly connected to the light emitting element,
• wherein the other of the source and the drain of the third transistor is connected to the third wiring,
• wherein one of a source and a drain of the fourth transistor is directly connected to the gate of the first transistor,
• wherein a gate insulating film is over a semiconductor layer,
• wherein a gate electrode of the first transistor and the first electrode of the capacitor over the gate insulating film,
• wherein an interlayer insulating film is over the gate electrode of the first transistor and the first electrode of the capacitor,
• wherein the second electrode of the capacitor is over the interlayer insulating film,
• wherein the first electrode of the capacitor overlaps the semiconductor layer, and
• wherein the second electrode of the capacitor is in contact with the semiconductor layer,
• wherein the capacitor has a first capacitance formed by the first electrode and the second electrode and a second capacitance formed by the first electrode and a part of the semiconductor layer.