We describe a technique for creating a thin polystyrene film containing a periodic array of cylindrical holes, with a hole size of approximately 13 nm and a lattice constant of 27 nm. The starting material is a polystyrene‐polybutadiene diblock copolymer, which self‐assembles into a hexagonally packed array of polybutadiene cylinders embedded in a polystyrene matrix. A technique described previously is used to orient the cylinders normal to the plane of the film. The polybutadiene domains are then removed by reaction with ozone, which attacks the double bonds in the polybutadiene backbone. Films of this type could potentially be used as templates for nanolithography on a scale not readily accessed by other techniques. ©1996 American Institute of Physics.