Deep etch x‐ray lithography permits the manufacture of very accurate high‐aspect‐ratio microstructures, which can be used as master templates for subsequent replication by electroforming and/or molding processes. This allows for mass production of three‐dimensional microstructures in a variety of materials. In this article we report on the first results using x rays from the Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory, as well as on the processing and technology developed to produce high‐aspect‐ratio microstructures. The first masks used were simple stencil masks chemically or laser etched in thick metal sheets. For resist, we used commercial acrylic cast sheets. Microstructures 840 μm thick were fabricated by deep x‐ray lithography and used as templates for copper electroforming. A technology for the high contrast masks required to work at these short wavelengths is being developed and a deep etch x‐ray lithography facility is under construction at the ALS.