We report on the initial stages of ZnO Atomic Layer Deposition (ALD) on In 0.53 Ga 0.47 As (InGaAs), studied by monitoring the ZnO film thickness in situ with spectroscopic ellipsometry. Using diethylzinc (DEZn) and water, at a substrate temperature equal to 120 • C, we found the presence of two different ZnO growth regimes prior to the steady growth: a slow ZnO nucleation on InGaAs, 0.005 nm.cy −1 (growth delay), then a substrate inhibited growth of type II. Increasing the DEZn injection time, the growth delay shortened from 30 cycles down to 3 cycles, concomitantly the steady growth rate increased from 0.18 to 0.23 nm.cy −1. The DEZn residence time and pressure increase during the first ALD cycle, allowing to suppress the growth delay, instead, no change is observed when performing the same experiment with water. Atomic Force Microscopy (AFM) images showed that the InGaAs surface roughened after the first cycle with a long DEZn pulse and residence time. The rough surface is likely at the origin of the growth delay elimination.