We obtained a bistable laser diode with a saturable absorber operating at a high repetition rate. The laser was made with a semi-insulating layer, which realised low carrier density in the reset region and low parasitic capacitance (3 pF over 300 μm). Low carrier density in the reset region where there is high differential gain (loss) reduces the carrier density changes caused by electrical reset and optical set signals. These enable flip-flop operation at a 2.5 Gb/s repetition rate.