Chemically treated InP(100) surfaces in aqueous HCl (0.009 less than or equal to x less than or equal to 36 wt %) solutions at 20 degrees C have been studied using X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), and contact-angle measurements. The XPS data indicate that the solutions cause the removal of the native oxide and leave behind an InP surface terminated by atomic chlorine. The SE data also suggest the immediate removal of the native oxide upon immersing the sample in the solutions. Longer immersion in the concentrated HCl solutions results in surface roughening; the roughened layer thickness obtained in the x = 12 wt % Cl solution for t = 6000 s, for example, is similar to 6 nm. Such SE-estimated surface roughness Values are considerably larger than the AFM rms values; the difference is considered to be due to the SE technique being sensitive to both the surface microroughness and the adsorbed chemical species. The HCl-cleaned InP surface is hydrophobic, The adsorbed Cl species may be the cause for the hydrophobicity.