A reference leak includes a leak layer formed of one of a metallic material, a glass material, and a ceramic material. The metallic material is selected from the group consisting of copper, nickel, and molybdenum. The leak layer comprises a number of substantially parallel leak through holes defined therein. The leak through holes may be cylindrical holes or polyhedrical holes. A length of each of the leak through holes is preferably not less than 20 times a diameter thereof. A diameter of each of the leak through holes is generally in the range from 10 nm to 500 nm. A length of each of the leak through holes is generally in the range from 100 nm to 100 .mu.m. A leak rate of the reference leak is in the range from 10.sup.-8 to 10.sup.-15 tor.times.l/s. The leak through holes have substantially same length and diameter.