A PIN diode is formed on an insulating structure on a substrate of semiconductor. The insulating structure is disposed on a high voltage doped region in the substrate. The PIN diode includes a semiconductor layer, disposed on the insulating structure. The semiconductor layer includes a first doped region of a first conductivity type, at least one second doped region of a second conductivity type, and at least one intrinsic region without being doped or lightly doped between the first doped region and the at least one second doped region. The first conductive type is opposite to the second conductivity type. At least one interconnection structure is disposed on the insulating structure to electrically connect the at least one intrinsic region to the high voltage doped well.