ZnSe single crystals were grown on a ZnSe(1 1 1)A seed from Se/Te mixed solutions. Effect of the thickness of the solution between a seed crystal and a source crystal on ZnSe crystals grown by the temperature gradient solution (TGS) method was studied for various distances. For the range of the solution thickness studied here (0.1-80 mm), the growth rate strongly depended on this thickness. Single crystals were obtained when the solution thickness was either 2 mm or less, or 30 mm or more, whereas polycrystals were obtained when the thickness was between 5 and 20 mm. The grown single crystals were characterized by using X-ray diffraction (XRD), photoluminescence (PL) at 4.2 K, and inductively coupled plasma mass spectrometry (ICP-MS). When a Se/Te solution was used, a solution thickness of either 0.5 or 50 mm produced grown-single crystals with the same crystallographic quality; the value of the full width at half maximum (FWHM) of X-ray rocking curve (XRC) was 5.2-6.0 arcsec, the lattice parameter was 5.6705 Angstrom measured by the Bond method, the Te concentration in the grown crystals was 0.12% (measured by using ICP-MS), and the PL spectrum was dominated by the emission from the Te isoelectronic trap of 2.69 eV. Our results show that the crystal growth changed from convection-limited to diffusion-limited depending on the solution thickness and that high-quality ZnSe single crystals can be grown by this TGS method.