An embodiment of an array of Geiger-mode avalanche photodiodes, wherein each photodiode is formed by a body of semiconductor material, having a first conductivity type, housing a first cathode region, of the second conductivity type, and facing a surface of the body, an anode region, having the first conductivity type and a higher doping level than the body, extending inside the body, and facing the surface laterally to the first cathode region and at a distance therefrom, and an insulation region extending through the body and insulating an active area from the rest of the body, the active area housing the first cathode region and the anode region. The insulation region is formed by a mirror region of metal material, a channel-stopper region having the second conductivity type, surrounding the mirror region, and a coating region, of dielectric material, arranged between the mirror region and the channel-stopper region.