In this letter, a method is outlined and results presented for an x‐ray lithography micromachining process that offers a greatly improved sensitivity over the LIGA process. This process is based on photosensitive polyimide (PPI), which is a commercial photoresist typically used as a passivation layer or dielectric material in the semiconductor industry. The main benefit of this process is its high sensitivity, which is approximately two orders of magnitude greater than that of the PMMA used in the LIGA process. Using a synchrotron radiation x‐ray source, we have achieved resist patterns over 1000 &mgr;m thick. The capability has also been demonstrated for aspect ratios over 10, as well as the ability to print linewidths down to 0.5 &mgr;m. ©1995 American Institute of Physics.