An apparatus and method for continuously monitoring the liquid nitrogen level a liquid nitrogen container and automatically refilling liquid nitrogen from a liquid nitrogen reservoir when the liquid nitrogen in the container falls below a predetermined level. The apparatus comprises a liquid nitrogen level sensing element, which contains a superconducting material, such as a YbaCuO type superconductiing material, disposed on a non-conducting substrate, such as magnesium oxide. The superconducting material is selected such that it has a critical temperature approximately equal to the boiling point temperature of liquid nitrogen. The superconducting material is placed near the predetermined level and, under normal conditions, the superconducting material exhibits zero or near zero resistance. When the level of liquid nitrogen falls below the predetermined level due to heat loss or other reasons, the resistance of the superconducting material will increase substantially, thus triggering a control means to open a solenoid valve and allow liquid nitrogen to flow from the reservoir to the container. The liquid nitrogen level sensing element can be prepared by photochemically etching a superconducting layer, which has been deposited on the non-conducting substrate, in accordance with a serpentine design, to thereby increase the sensitivity and reliability thereof.