The effects of several chemical treatments on ZnSe surface composition and morphology have been analyzed with scanning electron microscopy and Auger electron spectroscopy. Polycrystalline bulk and thin film ZnSe heteroepitaxed onto GaAs were used. Large variations in the etching rate and surface conditions, such as roughness, contamination, oxides, and stoichiometry, have been observed with different etchants. Contamination by carbon and oxygen was present on all the treated surfaces. Surface oxides could be thinned by dipping in HF or HF/H4Cl, which did not etch ZnSe. Methanol with 1% bromine etched ZnSe vigorously and selectively, and resulted in a rough surface. A relatively smooth ZnSe surface resulted from etching in NH4OH/H2O2, but excess Se precipitated from this solution to form whiskers. These whiskers could be removed using CS2. No excess Se was found after etching in hot NaOH but a thicker oxide and a pitted, rough surface was observed. A two stage etch consisting of NH4OH/H2O2 followed by CS2 is recommended for a smooth,near-stoichiometric surface.