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We present a new kind of rapid-single-flux-quantum (RSFQ) output driver together with a pseudomorphic high electron mobility transistor (p-HEMT) amplifier both operating at liquid helium temperature. The passive interconnect including the interchip connection between the RSFQ output driver and the first transistor stage of the semiconductor amplifier is the key element for signal matching and was optimized for minimizing the reflections to the RSFQ circuit. The RSFQ output driver is based on a single-flux-quantum to dc converter and a voltage doubler. The circuit is realized in the Niobium based 1 kA/cm2 process of FLUXONICS Foundry and provides up to 438-muV output voltage. We demonstrate high-speed experiments of the output driver in combination with two different semiconductor amplifier circuits at liquid helium temperature. The output voltage of a 2-Gb/s data stream was measured to be about 3.5 mV.