Surface-relief hexagonal-array diffraction gratings have been produced by three-beam coherent exposure. Collimated light was used in an attempt to produce a uniform relief profile over the total area of a 7.6-cm plate coated with a positive photoresist. The resulting gratings were reproduced in nickel by an electroforming process and analyzed by atomic force microscopy. The topography of the gratings was found to be that predicted by theory. The results obtained show that the gratings were of uniform profile over their total area.