We report the first results on superlattice modulation-doped field-effect-transistors (FET’s) fabricated using self-aligned gate by the ion-implantation process. The charge control superlattice layers consisted of Si-doped GaAs (N=4×1018/cm3) and undoped Al0.36Ga0.64As of period 50 Å. 1 μ gate enhancement-mode MODFET’s exhibited an extrinsic transconductance as high as 335 mS/mm and a source resistance of 0.7 Ω mm at 300 K. From x-ray diffraction analysis, conventional furnace anneal was found to intermix the superlattice layers. However, sharp 〈200〉x-ray diffraction satellite peaks were preserved after rapid anneal, which indicate that rapid thermal annealing does not degrade the structures significantly. Photoluminescence analysis indicated a shift in the emission peak of only 15 meV at 300 K, indicating interfacial broadening of less than one monolayer. Shifts in the threshold voltage Vt in these superlattice MODFET’s in the temperature range of 300–77 K were reduced to a range of 100–140 mV, as compared to standard n-(Al, Ga)As/GaAs MODFET’s with 140–300 mV shifts. The Vt shift in the superlattice MODFET’s suggests the possibility of effects of residual ‘‘DX’’ traps.