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A new circuit-level single-event upset (SEU) hardening approach for high-speed SiGe HBT current-steering digital logic is introduced and analyzed using both device and circuit simulations. The workhorse D-type flip-flop circuit architecture is modified in order to significantly improve its SEU immunity. Partial elimination of the effect of cross-coupling at the transistor level in the storage cell of this new circuit decreases its vulnerability to SEU. The SEU response of this new circuit is quantitatively compared with three other D flip-flop architectures, including the unhardened circuit, a conventional NAND gate based circuit, and a current-sharing hardened (CSH) circuit, at both variable data rate and switching current. The new circuit shows substantial improvement in SEU response over the unhardened version, with little increase in layout complexity and power consumption. While the NAND gate based circuit still shows better SEU response than the other circuits, its high power consumption will preclude its use in space applications. Our results suggest that this new circuit architecture exhibits sufficient SEU tolerance, low layout complexity, and modest power consumption, and thus should prove suitable for many space applications requiring very high-speed digital logic.