The interface morphology of gold contacts on ultrahigh vacuum (UHV) cleaved, air‐exposed, and chemically prepared GaAs surfaces has been studied by electron microscopy. Diodes formed on atomically clean cleaved (110) GaAs surfaces, subsequently annealed at 405 °C, were found to have flat interfaces. In contrast, diodes formed on air‐exposed and chemically prepared GaAs surfaces, also subsequently annealed at 405 °C, were found to have rough and uneven interfaces with a large number of protrusions extending into the semiconductor. They have different orientation relationships with the GaAs substrate than the diodes prepared in situ in UHV. The results of this study show that, upon annealing, the interfacial chemistry and morphology depend strongly on the surface preparation of GaAs before gold deposition.