A semiconductor device capable of dissipating heat, which has been produced in an ESD protection element, to the exterior of the device rapidly and efficiently includes an ESD protection element having a drain region, a source region and a gate electrode, and a thermal diffusion portion. The thermal diffusion portion, which has been formed on the drain region, has a metal layer electrically connected to a pad, and contacts connecting the drain region and metal layer. The metal layer has a first wiring trace extending along the gate electrode, and second wiring traces intersecting the first wiring trace perpendicularly. The contacts are connected to intersections between the first wiring trace and the second wiring traces. Heat that has been produced at a pn-junction of the ESD protection element and transferred through a contact is diffused simultaneously in three directions through the first wiring trace and second wiring trace in the metal layer and is released into the pad.