Provided is a semiconductor photoelectrode comprising a first conductive layer; a first n-type semiconductor layer disposed on the first conductive layer; and a second conductive layer covering the first n-type semiconductor layer. The first n-type semiconductor layer has a first n-type surface region and a second n-type surface region. The first n-type surface region is in contact with the first conductive layer. The second n-type surface region is in contact with the second conductive layer. The first n-type semiconductor layer is formed of at least one selected from the group consisting of a nitride semiconductor and an oxynitride semiconductor. The second conductive layer is light-transmissive. The second conductive layer is formed of a p-type oxide conductor.