The study of the degradation of silicon solar cells submitted to reverse bias stress is of crucial importance since the reliability of an entire PV system can be affected by the presence of weak paths (“hot spots”) on a single solar cell. This paper presents an analysis of the degradation of Metal Wrap Trough solar cells submitted to reverse bias step-stress. We show that the critical sites are in correspondence of the via-holes that connect the top-side metal lines to the back of the cell. Results show that the reverse current flow may induce modification of the shunt resistance of the cells, due to instabilities of the parasitic leakage paths which can be identified by thermal images.