While the cleaving process used for semiconductor Fabry–Pe´rot lasers produces atomically abrupt mirrors, there is considerable interest in mirrors defined by etching. Depending on the etching process employed, disorder of varying nature and degree results at the semiconductor–air interface. A theoretical approach capable of quantifying the impact of such disorder on the mirror reflectivity, to which laser performance is intimately connected, is presented. The theoretical technique is time‐dependent to facilitate visualization of the scattering process and is based on a locally one‐dimensional implicit‐finite‐difference approximation to the two‐dimensional scalar wave equation with variable coefficients. Mirror disorder is described in terms of a feature depth parameter and an in‐plane correlation length. The reflectivity falls off exponentially with disorder yet is found to remain close to its unperturbed value for the disorder scale attainable with the state‐of‐the‐art etching technology. ©1995 American Institute of Physics.