In this paper, a novel design of interconnect structure for CPW to CPW using the vertical "coaxial transition" is presented. The signal continuity is greatly improved since the coaxial-type transition provides more return current paths compared to the conventional transition using solder bumps. The design criteria of the vertical coaxial transitions for high frequency applications are described, and the key parameters in the coaxial transition structure are also discussed. CPW-to-CPW interconnect structure using the proposed coaxial transition was in-house fabricated. With proper design, the coaxial transition exhibits much better performance than the conventional one for very broadband applications.