A probe-on-carrier architecture is provided, where several vertical probes are disposed on each probe carrier and the probe carriers are affixed to the space transformer. Each vertical probe has two flexible members. The first flexible member makes electrical contact to the space transformer. The second flexible member makes temporary electrical contact to the device under test. A mechanical stiffener can be used to deal with the possible lack of flatness and thermal expansion of the space transformer. The mechanical stiffener can be affixed to the space transformer to bring the flatness and thermal expansion of the space transformer to within specifications. Alternatively, the mechanical stiffener can be affixed to the space transformer without trying to bring the flatness and thermal expansion of the space transformer to within specifications.