An ultra-high pressure mercury lamp is provided in which the disadvantage caused by projections formed on the electrode tips during operation can be eliminated. This is achieved by an arrangement in which a silica glass arc tube, filled with at least 0.15 mg/mm.sup.3 of mercury, rare gas and halogen in the range from 10.sup.-6 .mu.mole/mm.sup.3 to 10.sup.-2 .mu.mole/mm.sup.3, includes a pair of opposed electrodes spaced a distance of at most 2 mm. Additionally, at least one of the electrodes includes a part with a greater diameter which is formed on the electrode shaft using a melting process, a projection which is formed by the tip of the electrode shaft, and a part with a decreasing diameter which extends from the part with the greater diameter in the direction toward the projection.