We have performed total-energy density-functional calculations using ab initio pseudopotentials to investigate the atomic geometry and scanning tunneling microscopy (STM) of K adsorbed on the InAs(1 1 0) surface. We have identified the most favorable adsorption geometry formed by K adatoms occupying two almost degenerate adsorption sites. Based on this structure, we have simulated the STM images showing asymmetric and zigzag chain along the [110] direction for both negative and positive sample biases. The calculated STM images agree with the recent STM observation. (C) 2004 Elsevier B.V. All rights reserved.