Self-assembled Ge islands are weakly ordered along the intrinsic step direction when grown directly on well-prepared biatomic-stepped vicinal Si(001) surfaces. Prominent two-dimensional ordering of Ge islands is realized when a SiGe/Si multilayer is predeposited on such vicinal Si(001) surfaces and step-bunching takes place. The ordering helps to narrow the size distribution of the Ge islands. This provides an effective method for controlling the Ge islands in both ordering and size.