We present a gate-recess structure for 0.1 mu m metamorphic high-electron-mobility transistors to enhance the maximum frequency of oscillation (f(max)). Among the established gate-recess structures, the narrow gate-recess structure shows a degraded f(max), despite superior dc characteristics due to a large gate-to-drain capacitance (C-gd) caused by a small effective gate-to-drain spacing, while the wide gate-recess structure exhibits lower dc characteristics due to the surface effects. To minimize C-gd and maintain the dc characteristics of the narrow gate-recess structure, an additional gate-recess is performed for an electrical isolation between the drain side cap layer and drain electrode. We obtain almost the same extrinsic transconductance of similar to 600 mS/mm from this, while we achieve similar to 18% enhancement of f(max) (similar to 317 GHz) due to similar to 16% reduction of C-gd by the increase of effective gate-to-drain spacing compared to the narrow gate-recess structure. (C) 2008 The Electrochemical Society. [DOI: 10.1149/1.2992083] All rights reserved.