In this work the local values of contact potential difference (CPD) and their distributions in the plane of the metal-insulator-semiconductor (MIS) structure's gate have been determined for the first time. This has been achieved by application of a focused beam of UV radiation from a laser source. The less than 20-mum diameter of UV radiation beam allows determination of distributions of local CPD values in the plane of the gate. The CPD distribution is such that its values are highest far away from the gate edge regions, lower in the vicinity of gate edges and still lower in the vicinity of gate corners. In this paper the method and the optical setup used to determine local values of CPD are described and example measurement results are given. The CPD distributions obtained have been confirmed by a series of independent measurements by other methods. It is believed that the CPD distributions obtained (as well as distributions of local values of other parameters) are due to the mechanical stress distributions under the gate of a MIS system. (C) 2003 Elsevier B.V. All rights reserved.