A semiconductor device structure includes a semiconductor substrate with an active region provided therein, a gate structure, a dummy gate structure and two contact regions provided in the active region for forming source and drain regions. The gate structure and the dummy gate structure are formed on the semiconductor substrate so as to partially overlie the active region, and one of the contact regions is located at one side of the dummy gate structure. The semiconductor device structure includes a contact structure contacting one of the contact regions and the dummy gate for connecting this contact region and the dummy gate to one of a Vdd rail and a Vss rail. The active region has an extension portion protruding laterally away from the active region relative to the other contact region, where the contact structure is located over the extension portion.