An extremely high vacuum chamber for the calibration of ultrahigh vacuum gauges was fabricated and tested. The chamber has an inner diameter of 250 mm and is 1800 mm long. It has 20 gauge ports and a liquid-nitrogen shroud inside to suppress interference between gauges and to avoid pressure rise due to thermal radiation from the gauges. The vacuum chamber was made of specially extruded aluminum alloy A6063-T6-EX in an oxygen and argon atmosphere. The chamber was assembled using tungsten inert gas welding in an argon atmosphere. After a bakeout at 150 °C for 24 h, a specific outgassing rate of the order of 10−13 Torr l/s cm2 was obtained. The system was evacuated with a turbobacked 300 l/s turbomolecular pump. The extremely high vacuum is maintained by two 300 l/s sputter ion pumps and a titanium sublimation pump with a liquid-nitrogen shroud. These pumps are also made of aluminum alloys. An ultimate pressure of 3×10−13 Torr was measured with a point collector gauge with spherical anode. Residual gas analysis in the 3×10−12 Torr was performed by a newly developed Q-mass filter.