A semiconductor element including: an element substrate provided with an element region at a middle part and a peripheral region outside the element region; and a readout circuit substrate facing the element substrate, in which the element substrate includes a first semiconductor layer provided in the element region and including a compound semiconductor material, a wiring layer provided between the first semiconductor layer and the readout circuit substrate, the wiring layer electrically coupling the first semiconductor layer and the readout circuit substrate to each other, a first passivation film provided between the wiring layer and the first semiconductor layer, and a second passivation film opposed to the first passivation film with the first semiconductor layer interposed therebetween, and in which the peripheral region of the element substrate includes a bonded surface with respect to the readout circuit substrate.