A testing head comprises a plurality of contact probes, and a guide having a plurality of guide holes for housing the contact probes and including a conductive portion. Each contact probe includes a first end region and a second end region, and a body which extends between the first and second end regions. Suitably, the conductive portion includes a group of the guide holes and electrically connects contact probes of a first group of the contact probes. The contact probes of the first group slide in the guide holes in the conductive portion and are adapted to carry a same signal, and each contact probe of a second group of the plurality of contact probes is surrounded by an insulating coating layer that extends along the body of each contact probe of the second group, thereby insulating the contact probes of the second group from the conductive portion.