Functional 150‐nm gate‐length high electron mobility transistors (HEMTs) have been successfully fabricated using storage ring x‐ray lithography (XRL) for all process levels. This article describes the L2M XRL exposure system including x‐ray masks, the planar‐doped GaAlAs/GaAs HEMT fabrication process, and the characteristics of the resulting devices. The gate length, a key device performance parameter, was minimized down to 150 nm using an optimized chemically amplified SAL601 negative resist process at small proximity gap (≤20 μm). This optimization process indicates that process latitude and resolution are primarily limited by the post‐exposure bake (PEB) step which has been adjusted to 95 °C. The fabricated HEMTs have excellent dc characteristics with a peak extrinsic transconductance as high as 400 mS/mm.