A semiconductor device comprising: a first line being a current supply line; a second line being a source signal line; a first transistor; a second transistor; a third transistor; a fourth transistor; a capacitor; and an EL element, wherein one of a source and a drain of the first transistor is electrically connected to the EL element so that a current from one of the source and the drain of the first transistor flows through the EL element, wherein a gate of the first transistor is electrically connected to a gate of the second transistor so that a first voltage at the gate of the first transistor is applied at the gate of the second transistor, wherein one of a source and a drain of the second transistor is electrically connected to the first line, wherein the other of the source and the drain of the first transistor is electrically connected to the other of the source and the drain of the second transistor so that a second voltage at the other of the source and the drain of the first transistor is applied at the other of the source and the drain of the second transistor, and wherein one of a source and a drain of the third transistor is electrically connected to the other of the source and the drain of the second transistor so that a third voltage at the one of the source and the drain of the third transistor is applied at the other of the source and the drain of the second transistor characterized by a third line; and a fourth line; wherein a gate of the third transistor is connected to the third line; wherein a gate of the fourth transistor is connected to the fourth line; wherein a first terminal of the capacitor is connected to the first line and a second terminal of the capacitor is connected to a gate of the first transistor, a gate of the second transistor and one of a source and a drain of the fourth transistor; wherein the other of the source and the drain of the fourth transistor is connected to the second line; and wherein the other of the source and the drain of the third transistor is connected to the second line. a first line being a current supply line; a second line being a source signal line; a first transistor; a second transistor; a third transistor; a fourth transistor; a capacitor; and an EL element, wherein one of a source and a drain of the first transistor is electrically connected to the EL element so that a current from one of the source and the drain of the first transistor flows through the EL element, wherein a gate of the first transistor is electrically connected to a gate of the second transistor so that a first voltage at the gate of the first transistor is applied at the gate of the second transistor, wherein one of a source and a drain of the second transistor is electrically connected to the first line, wherein the other of the source and the drain of the first transistor is electrically connected to the other of the source and the drain of the second transistor so that a second voltage at the other of the source and the drain of the first transistor is applied at the other of the source and the drain of the second transistor, and wherein one of a source and a drain of the third transistor is electrically connected to the other of the source and the drain of the second transistor so that a third voltage at the one of the source and the drain of the third transistor is applied at the other of the source and the drain of the second transistor characterized by a third line; and a fourth line; wherein a gate of the third transistor is connected to the third line; wherein a gate of the fourth transistor is connected to the fourth line; wherein a first terminal of the capacitor is connected to the first line and a second terminal of the capacitor is connected to a gate of the first transistor, a gate of the second transistor and one of a source and a drain of the fourth transistor; wherein the other of the source and the drain of the fourth transistor is connected to the second line; and wherein the other of the source and the drain of the third transistor is connected to the second line.