A testing head for testing a device includes a couple of plate-like supports separated from each other by a suitable gap and provided with respective guide holes to slidably house a plurality of contact probes, each including a rod-like body extending along a preset longitudinal axis between a first and second ends, the first end being a contact tip that abuts a contact pad of the device and the second end being a contact head that abuts a contact pad of a space transformer. At least one of the supports comprises a couple of guides that are parallel to each other and separated by an additional gap and provided with corresponding guide holes. Each contact probe comprises a protruding element or stopper originating from a lateral wall and realized in correspondence of one wall of a guide hole of the guides contacting the lateral wall of the contact probe.