We have printed dense line/space patterns with half-pitches as small as 12.5 nm in a negative-tone calixarene resist using extreme ultraviolet (EUV) interference lithography. The EUV interference setup which is based on transmission diffraction gratings is illuminated with spatially coherent radiation from a synchrotron source. The results show the extenclibility of EUV lithography to printing features measuring less than 15 nm in size. We discuss the potential impact of effects such as photoelectron blur and shot noise in high-resolution EUV lithography. (c) 2007 American Vacuum Society.