The Soufrière of Guadeloupe lava dome consists of several 3D domains of relatively unaltered massive andesite separated by major radial fractures that reach at least up to about half of the dome's height. More than 20,000 geo-electrical measurements made on the top and the flanks of the lava dome are used to construct the first geophysical image of the internal structure of this active volcano. The main features of the apparent conductivity structure of the lava dome are high-conductivity regions associated with the strongly altered material of present and fossil hydrothermal zones. Local 1D inversions of data subsets belonging to regions where the geological structure is supposed laterally invariant confirm the structures observed in the pseudo-sections. The relatively stable units lie above a basal inclined layer of highly conductive geological materials interpreted to be more altered and thus characterised by reduced internal friction and probably increased pore pressure. Past and current hydrothermal fluid circulation through these fractures has promoted rock alteration and particularly along the base of the dome that likely contributes to the instability of parts of the edifice.