An alignment mark on a wafer is described, including at least one dense pattern and at least one block-like pattern adjacent thereto and shown as at least one dark image and at least one bright image adjacent thereto. A method of getting a position reference for a wafer is also described. An above alignment mark is formed. The alignment mark, which is shown as at least one dark image and at least one bright image adjacent thereto that are formed by the at least one dense pattern and the at least one block-like pattern, is then detected.