Reducing hillock surface defects, which are often present with a density larger than 10(3) cm(-3) on HgCdTe grown on (100) GaAs by metal organic vapor phase epitaxy, is the most difficult task for many researchers. In order to improve the surface morphology of HgCdTe layers, the pre-reaction of the Cd precursor with Hg was suppressed by putting a lid on the heated Hg bath that was positioned in front of the susceptor. Hillock density was decreased by one order of magnitude using this procedure. HgCdTe layers also showed a better crystallinity. Our results show that HgCdTe layers with very small hillock densities, < 100 cm(-2), could be grown on (100) GaAs with a 4degrees misorientation toward <100> by suppressing the pre-reaction of Cd precursor with Hg, when combined with rinsing the substrate with KOH water solution. HgCdTe layers with good morphology could also be grown on (10 0) CdZnTe with a 4degrees misorientation toward <100>, when pre-reaction of the Cd precursor with Hg was suppressed. (C) 2002 Elsevier Science B.V. All rights reserved.