Scanning tunneling microscopy (STM) connected to molecular beam epitaxy is used to investigate InAs islanding on GaAs(0 0 1) substrates. From the time evolution of STM images taken for the surfaces covered with wetting layers and islands, it is found that InAs islanding initially occurs at monatomic steps on wetting layers, and that even at room temperature, monatomic steps move around. As a result, InAs islands are usually observed both on terraces and on steps by STM long after InAs growth. Moreover, islands are aligned with monatomic steps on vicinal GaAs(0 0 1) substrates inclined toward [1 1 0]. Our findings provide new insight into manipulating spatial arrangement of quantum dots by utilizing islanding of InAs.