For the study of the ultimate resolution limits of x-ray nanolithography, i.e., the contact printing of features smaller than 30 n m, the biggest task is the production of x-ray nanomasks. The fabrication of such conventional masks with features as small as 12 nm for isolated dots and 25 nm for isolated lines is reported. High-energy electron beam lithography, using a transmission electron microscope operating at a voltage of 200 kV was carried out in a 400-nm-thick single resist layer with an electron probe of 1 nn in diameter. The ability of gold plating to enter very narrow structures is demonstrated here : 12 nm width absorber features with a thickness of 360 nm are obtained. We demonstrate that sub-30 nm features can be routinely produced with aspect ratios as high as 15 with a good process latitude.