A capacitor having a discharge gap, which comprises a generally plate-like substrate having a pair of opposite major surfaces and having a portion cut away to define an opening, first and second capacitive electrodes formed on the respective major surfaces of the substrate, and first and second discharge electrodes electrically connected with the first and second capacitive electrodes, respectively. The first and second discharge electrodes are positioned on respective sides of the opening in the substrate so as to confront each other across a discharge gap which includes the width and the thickness of the opening.