A masking device for performing high-resolution photoresist-based lithography in the fabrication of integrated circuits. The heart of the device is a cylindrical block made of material transparent to, and manifesting a relatively high index of refraction for, the wavelengths of light to be used in conjunction with it. The mask end of the block is imprinted with a pattern of ridges corresponding to the pattern to be illuminated on the photoresist. The mask end, including the inter-ridge troughs, is covered with a metal film several tens of .ANG. thick. The troughs are filled in with a material such as carbon black strongly absorptive of the wavelengths that will emerge from the mask. The sides of the block are covered with a metal cladding sufficiently thick to prevent any light from escaping from the block. The top end of the block, opposite the mask end, is left uncovered. In operation, the block is used in conjunction with a precise positioning mechanism for locating the block in the horizontal plane and for maintaining a very small, but non-zero, distance between the mask ridges and the photoresist layer, such that the photoresist layer is in the near-field of the mask. In this manner, the photoresist can be illuminated with the pattern desired, with a resolution sufficient to produce circuit elements with dimensions much less than the wavelength of light entering the top end of the mask block.