A simple Cl2/Ar plasma chemistry without additional sample heating is found to produce etch rates above 1 μm/min for InP under high microwave power (1000 W) electron cyclotron resonance conditions. While the etch rate increases essentially linearly with Cl2 composition the root‐mean‐square (RMS) surface roughness measured by atomic force microscopy is strongly dependent on the Cl2‐to‐Ar ratio. Under optimized conditions (10Cl2/5Ar), RMS roughness of ∼2.6 nm is obtained on samples etched more than 1 μm, a typical unetched control sample displays a RMS value of 1.3–1.6 nm. The high ion current under ECR conditions appears to promote efficient sputter desorption of the InCl3 etch product and prevents buildup of the usual selvedge layer that requires elevated sample temperatures to desorb under more conventional reactive ion etching conditions. The result is a simplified plasma chemistry with avoidance of the polymer deposition and hydrogen passivation associated with CH4/H2 discharges.