A reduction is achieved in the power consumption of a solid-state imaging element including a photoelectric conversion element which converts incident light to charge and a transistor which converts the charge obtained in the photoelectric conversion element to voltage. A photodiode and a charge read transistor which are included in a pixel in the CMOS solid-state imaging element are provided in a semiconductor substrate, while an amplification transistor included in the foregoing pixel is provided in a semiconductor layer provided over the semiconductor substrate via a buried insulating layer. In the semiconductor substrate located in a buried insulating layer region, a p+-type back-gate semiconductor region for controlling a threshold voltage of the amplification transistor is provided.