We have developed a simple experimental technique for measuring the absorption spectrum of x‐ray photoresists in the region from 1000 to 3000 eV. Knowledge of the absorption characteristics of a photoresist allows selection of the most efficient range of energies to use for performing x‐ray exposures. The measurements were performed using the Medical Physics beamline on the University of Wisconsin Aladdin synchrotron source. The beamline is equipped with a lithium‐drifted silicon detector that provides an energy resolution of 150 eV. To avoid saturation of the Si(Li) detector, special ‘‘microbeams’’ of approximately 50 circulating electrons in the storage ring were employed. The beam intensity was monitored using a photodiode. The operation of the detector and associated diagnostic equipment will be described. Four by four millimeter square, 1.4 μm thick silicon nitride membranes were used as substrates for the resist films. Photoresist absorption was measured by comparing the transmission of silicon nitride membranes with and without photoresist coatings. Experimental results for both conventional and chemically amplified positive and chemically amplified negative x‐ray photoresists are presented.