Patent ID: 8243415

Claim:
An ignition plug comprising: a center electrode; a substantially tubular insulator having an axial bore extending in a direction of an axis of the center electrode, and holding the center electrode in the axial bore; and a ground electrode disposed in contact with a front end portion of the insulator and having a through-hole; wherein a front end portion of the center electrode is located rearward of the front end portion of the insulator, a semiconductor layer in contact with the center electrode and the ground electrode, said semiconductor layer being formed along a portion of a surface of the insulator, at least a portion of a surface of the ground electrode is in contact with the front end portion of the insulator via the semiconductor layer, and the portion of the ground electrode which is in contact with the front end portion of the insulator via the semiconductor layer extends at least 0.1 mm radially outward from a circumference of the through-hole.