We present microwave (MW) design, characterization, and modeling of a dip probe that can deliver ultrashort electrical pulses to semiconductor nanodevices at cryogenic temperatures (T). Systematic MW measurements, equivalent circuit modeling, and parameter extraction of the superconducting coaxial cable, in which there is a T gradient from 300 to 4.2 K, are successfully performed. De-embedding of the MW sample mounting stage (SMS) characteristic from measurement results of the dip probe dipped in liquid He is achieved using this cable modeling. The de-embedded 4.2 K characteristic of the MW SMS is in reasonable agreement with the result of three-dimensional field simulation. Finally, transmission of short electrical pulses from the pulse generator at 300 K to the MW SMS at 4.2 K, with minimal degradation, is successfully demonstrated using our dip probe. Our design and characterization technique can be applied to almost all cryogenic equipment for MW characterization. © 2004 American Institute of Physics.