We have combined a cryogenic BiCMOS integrated circuit with a superconducting Josephson junction array. The BiCMOS circuit serves as an on-chip pulse generator delivering return-to-zero pulses with pulse frequencies of up to 15 GHz. With this microwave drive, we observe wide and flat Shapiro steps in the voltage-versus-current characteristics of the Josephson junction array. To the best of our knowledge, this is the first integration of a Josephson junction array with a cryogenic BiCMOS chip. Our results pave the way to a hybrid and fully integrated Josephson arbitrary waveform synthesizer with possible applications in quantum electronics and quantum voltage metrology.