We present a coplanar flip‐chip mounting technique for broadband microwave and high‐speed opto‐electronic devices. The technique is based on coplanar waveguides with tapered structures that can be fabricated with high precision by photolithographic means on planar dielectric substrates and device chips. It allows the inclusion of micrometer size devices into broadband circuits and serves for the transmission of high‐speed signals with low reflection over waveguides with varying geometry and to external coaxial lines with millimeter dimensions. As demonstrated by flip‐chip mounted high‐speed photoconductors, by a coplanar pulse‐forming circuit, and by a coplanar line termination, this technique allows broadband transmission with reflections not exceeding a few percent in the frequency range from dc to 25 GHz and signal durations at least as short as 20 ps.