A fully planar self-aligned technology with a standard photolithographic process has been used to fabricate binary frequency dividers on GaAs counting correctly from d.c. to over 5 GHz, which is the best performance so far on such circuits. The divider is an optimised version of the gated T master/slave flip-flop. The m.e.s.f.e.t.'s gates are 0.6 μm within 2 μm drain-source spacing.