Initial stages of self-assembled growth of InAs dots on GaAs(001) and a postgrowth evolution of the deposited surface have been investigated by reflectance-difference (RD) spectroscopy and reflection high-energy electron diffraction (RHEED). A significant change in the RD spectrum occurs even at 0.1-monolayer (ML) deposition of InAs. With increasing InAs deposition, the As-dimer-elated RD sign is inverted, which indicates that the original As dimer along the [110] direction of the c(4 x 4) As-rich GaAs(001) surface becomes dimerized along the [-110] direction. Postgrowth behavior has been studied at 480 degrees C after 1.9-ML deposition of InAs. During postgrowth, the As-dimer-related RD signal returns to signals observed at lower InAs deposition. This behavior gives evidence that the InAs coverage is reduced by postgrowth. Furthermore, positive offsets that increase in amplitude with photon energy appear in the RD spectra of the postgrown samples.