The reactive ion etching behavior of GaAs in Cl2and SiCl4gases is investigated with regard to the suitability of this process for etching through wafer via holes using a photoresist mask. The criteria used are etch rate, profile (wall angle), selectivity, undercut, and smoothness of the etch. The experimental points were chosen using aD‐optimal statistical design. The experimental results have been evaluated by multiple stepwise regression, eliminating insignificant terms from a quadratic model of the controlled parameters (mask bake time, power, pressure, chlorine flow, and etch time). Empirical models of the dc bias and each etch criterion are obtained. The highest etch rates, at over 3 μm/min, are obtained in high chlorine concentrations at high dc bias values (high power and low pressure) for short etch times. This method yielded an optimized process for etching metallizable via holes.