Probes are applied to pairs of contacts, and the resistance between them is measured by applying a voltage across the contacts and measuring the resulting current. The current flows from the first probe, into the metal contact, across the metal-semiconductor junction, through the sheet of semiconductor, across the metal-semiconductor junction again (except this time in the other direction), into the second contact, and from there into the second probe and into the external circuit to be measured by an ammeter. The resistance measured is a linear combination (sum) of the contact resistance of the first contact, the contact resistance of the second contact, and the sheet resistance of the semiconductor in-between the contacts.