A semiconductor device has: a power supply line; a ground line; a signal line for transmitting a signal; a signal pad connected to the signal line; a protection element connected between the signal line and the ground line; and a trigger circuit configured to supply a trigger current to the protection element. The trigger circuit has: a PMOS transistor whose gate and backgate are connected to the power supply line and whose source is connected to the protection element; and an amplifier circuit part configured to amplify a first current flowing through the PMOS transistor to generate a second current. The trigger current includes the second current.