Glass sealed gas discharge tubes. In some embodiments, a gas discharge tube (GDT) can include an insulator substrate having first and second sides and defining an opening. The GDT can further include a first electrode implemented to cover the opening on the first side of the insulator substrate, and a second electrode implemented to cover the opening on the second side of the insulator substrate. The GDT can further include a first glass seal implemented between the first electrode and the first side of the insulator substrate, and a second glass seal implemented between the second electrode and the second side of the insulator substrate, such that the first and second glass seals provide a hermetic seal for a chamber defined by the opening and the first and second electrodes.