In a semiconductor device, a first contact-diffusion-layer is in a first well to be connected to the first well and extends in a channel width direction of a first transistor in a first well. A second contact-diffusion-layer is in the first well so as to be electrically connected to the first well and extends in a channel-length direction of the first transistor. A first contact on the first contact-diffusion-layer has a shape with a diameter in the channel-width direction larger than that in the channel-length direction when viewed from above the substrate. A second contact on the second contact-diffusion-layer has a shape with a diameter in the channel-width direction smaller than that of the first contact and a diameter in the channel-length direction almost equal to that of the first contact when viewed from above the substrate. A wiring is electrically connected to the first transistor through the second contact.