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Short-channel effects of GaAs n+-gate self-aligned MESFET's are investigated for different n+-layer-gate gaps. The gate lengths range from 0.1 to 1.5 µm. The fabrication features are self-aligned implantation for n+-layer technology (SAINT) and an electron-beam direct writing. The n+-layer-gate gap is controlled by the undercut process in the bottom resist of a multilayer resist acting as n+ion implantation mask. It is shown that the short-channel effects such as an increase in subthreshold current and a negative shift of threshold voltage can be substantially alleviated by enlarging the n+-layer-gate gap from 0.15 to 0.3 µm.