  In this paper, we report on the method of nondestructive quality control that
can be used in fabrication of GaAs high-speed electronics. The method relies on
the surface potential mapping and enables rigid in vivo analysis of transport
properties of an active electronic device incorporated into a complex
integrated circuit. The study is inspired by our ongoing development of a
millimeter wave intelligent reflective surface for 6G communications. To
provide desired beamforming capabilities, such a surface should utilize
hundreds of identical microscale GaAs diode switches with series resistance of
a few ohms. Thus, we develop a ladder-like layered ohmic contact to heavily
Si-doped GaAs and cross-study it via transmission line method and Kelvin probe
force microscopy. The contact resistivity as low as 0.15~$\mu \Omega \,$cm$^2$
is measured resulting in only a 0.6~$\Omega$ of resistance for the contact area
of 3$\times$3~$\mu$m$^2$. Moreover, the tendencies observed suggest that one
can rigidly analyze the evolution of contact resistance and the profile of
resistivity under contact in response to rapid thermal annealing, once the
surface potential map across the ``ladder'' is known.
