In a method of manufacturing a photoelectric conversion device having a pixel region and a peripheral circuit region, a semiconductor compound layer is formed by causing a surface of a diffusion layer or gate electrode of a MOS transistor in the peripheral circuit region to react with a high melting point metal, then an insulating layer is formed in the pixel region and the peripheral circuit region after the step of forming a semiconductor compound layer. A contact hole is formed in the insulating layer to expose a diffusion layer in the pixel region, and a contact hole is formed in the insulating layer to expose the semiconductor compound layer formed in the peripheral circuit region. These holes are formed at different timings. Prior to forming the hole which is formed later, a contact plug is formed in the contact hole which is formed earlier.