We calculate the effects of facet roughness on laser performance of etched‐facet semiconductor diode lasers. Facet roughness can be caused by the finite pixel size, used in photolithographic mask fabrication, or in the facet etching process. We consider various sizes of roughness and show that appreciable effects can result from roughness levels previously considered optically flat. Far‐field shifts and modal coupling caused by facet roughness are also calculated. Results are highly useful for designing lasers with curved or arbitrarily oriented facts such as unstable resonators or beam steering fan laser diodes. ©1996 American Institute of Physics.