Example embodiments may provide a photodiode formed of semiconductor silicide and/or an image sensor using a photodiode formed of semiconductor silicide. The photodiode may have a p-n junction structure including a p-type semiconductor silicide and an n-type semiconductor silicide. The image sensor may include a substrate, a photodetector unit having the photodiode, which may perform photoelectric transformation, and/or a signal transmitter transmitting a signal generated by the photodetector unit to an output unit. The photodetector unit and/or the signal transmitter may be integrated in the substrate.