A modified photochemical-diode (PD) model, designated as a photochemical-corrosion-diode (PCD) model, was proposed for interpreting galvanic corrosion in metal-matrix composites (MMCs) containing semiconducting constituents. The characteristics of the PCD model were introduced through direct comparison with that of the PD model. The PCD model was then used to interpret galvanic corrosion in SiC-reinforced Al MMCs. The PCD model and the photoelectrochemical experiments on both Al/SiC MMCs and monolithic SiC predicted that solar irradiation may affect the corrosion of the Al/SiC MMCs, corroborating well with field experiments. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3232299] All rights reserved.