This study investigates the mechanism responsible for the electrochemical oscillations during silicon galvanostatic anodizing. Two oscillatory regimes of anodic silica formation in dilute fluoride electrolyte are monitored by combined in-situ curvature measurement and ellipsometry. At lower applied current density, a dense silica film is formed and the oscillations features are similar to those observed in fluoride-free electrolytes. At higher applied current density, a porous silica film is formed and the oscillations progressively reappear after a transition regime without oscillations. The disappearance and the reappearance of the oscillations are associated to variations of the degree of synchronization between the self-oscillating domains. In addition, the similarities between the oscillatory regimes and the persistence of sustained oscillations during the formation of thicker silica indicate that all oscillations arise from a same mechanism that survives the oxide accumulation at the silicon surface. (C) 2014 The Electrochemical Society. All rights reserved.