A spark plug, including an insulator embedding a first metallic electrode axially extending therethrough from a high voltage outer end terminal to the center of the inner end of the insulator from which it protrudes; a metallic ground electrode isolated from the first electrode and having an extended inner termination facing toward the first electrode extending from the insulator tip for defining therebetween a spark gap, a resistive element connected to the ground electrode such that upon mounting the spark plug in an internal combustion engine, the ground electrode electrically connects to the engine body through the resistive element; and a second outer termination of the ground electrode, adapted to constitute an accessible sensing terminal.