A multichamber ultrahigh vacuum (UHV) scanning tunneling microscope (STM) system which includes a molecular‐beam epitaxy (MBE) growth chamber, as well as a STM chamber, has been constructed for the investigation of processed GaAs surfaces. We observed MBE‐grown GaAs surfaces using this system. Samples were grown on GaAs (001) surfaces and cooled to certain temperatures in an As4flux before being transferred into an UHV. STM images ofc(4×4), 2×4, and mixedc(4×2) and 2×2 structures were obtained for the samples cooled to 330, 570, and 470 °C in an As4flux, respectively. The mixedc(4×2) and 2×2 structure seems to be formed by desorption of As atoms from thec(4×4) surface in an UHV. Also, a new reconstructed structure which has a 2.8‐nm periodicity along both the [110] and [11̄0]directions was observed. It seems to be a local structure which has a larger arsenic dimer density than that of thec(4×4) structure.