Abstract: A contactor structure employed in a high speed electronic test system for testing the electrical integrity of the conductive paths (or lines) in the packaging substrate prior to the mounting and connection thereto of the high circuit density monolithic devices. The contactor structure includes a semiconductor space transformer fabricated by large scale integration techniques and containing a plurality of discrete first integrated circuits. The first integrated circuits of the space transformer being respectively electrically connected to said electrical probes. Second integrated circuitry interconnecting said first integrated circuits is also contained within said semiconductor space transformer. Under control of said test system said second integrated circuitry selectively energizes, selected first and second ones of said first integrated circuits.