This invention aims at providing an inexpensive semiconductor device having a parasitic diode and lowering an hfe of a parasitic PNP transistor and a manufacturing method thereof. Such semiconductor device includes a P-type silicon substrate and a gate electrode formed above the P-type silicon substrate. The P-type silicon substrate includes an N-type well layer, an N-type buried layer, a P-type body layer, an N-type source layer formed in the P-type body layer, and a drain contact layer formed in the N-type well layer. The P-type body layer and the N-type source layer are formed by self alignment that uses the gate electrode as a mask. The N-type drain contact layer is formed opposite the N-type source layer across the P-type body layer formed below the gate electrode. The N-type buried layer is formed below the P-type body layer.