A laser‐induced dry etching process based on the generation of reactive species from the pyrolytic decomposition of selected metal alkyls is presented. Specifically, a focused, 514 nm cw laser to locally heat the surface of a GaAs sample in a dimethylzinc (DMZn) ambient is used. The DMZn dissociates pyrolytically at the hot surface, yielding reactive species that locally etch the GaAs. We have studied the process by characterizing etch rates in terms of laser dwell time, laser‐induced temperature, and DMZn pressure. Further, we have investigated the thermal dependence of the process, and have determined the boundaries of the parameter space for the successful avoidance of competing processes. Based on our experimental results and those of previous workers, we speculate that reactive methyl groups produced in the pyrolytic decomposition of DMZn react with the GaAs surface to produce volatile alkylated by‐products. Finally, the process to allow for the direct writing of surface‐relief features having smooth walls and submicron to micron‐scale depths have been optimized, which are potentially useful as electronic or optoelectronic device components. To demonstrate the utility of the etching process, riblike waveguiding structures in GaAs/Al0.3Ga0.7As multilayer substrates have been fabricated.