Ex-situ aqueous (NH4)(2)S treated sulfur-passivated InP substrates have been studied using ultrahigh vacuum scanning tunnelling microscopy (STM) and low-energy electron diffraction (LEED). The morphology of the passivated surface was imaged after a mild sample annealing. The STM images of a surface exhibiting a good 1x1 LEED pattern show that the top layer of the sulfur-passivated surface is poorly ordered. A surface bilayer atomic step has been observed to be common on sulfur-passivated surfaces. The magnitude of the surface roughness for the passivated surfaces lies between 10 Angstrom and 25 Angstrom; this is much smaller than the roughness of InP(100) substrates prepared using previously published methods. After annealing the sample at similar to 420 degrees C, a (2x1) LEED pattern with split half-integer spots has been observed. The associated STM images show that these split half-integer diffraction beams correspond to regularly spaced domains with a width of similar to 20-30 Angstrom in the [01(1) over bar] direction. The surface roughness increases with annealing temperature; the surface corresponding to the best 2x1 LEED symmetry (annealing at similar to 420 degrees C) has a roughness double that of the 1x1 phase.