A semiconductor device includes a lateral double diffused metal oxide semiconductor (LDMOS) , a junction field effect transistor (JFET) and an inner circuit. The lateral double diffused metal oxide semiconductor includes a first source, a common drain and a first gate. The junction field effect transistor includes a second source, the common drain and a second gate. The second source is electrically connected to the first gate. The inner circuit is electrically connected to the first source.