Patent ID: 7842967

Claim:
A semiconductor device used in a step-up DC-DC converter, comprising: a switching element; a diode element formed in the same semiconductor substrate as the switching element; a switching terminal; and an output terminal, wherein the switching element includes a LDMOS transistor having a channel region formed of a surface portion of a body diffusion layer below a gate electrode of the LDMOS, said LDMOS transistor including a source diffusion layer, wherein the body diffusion layer has a conductivity opposite to a conductivity of the source diffusion layer, and is formed to enclose a side surface and a bottom surface of the source diffusion layer, and a drain diffusion layer that has a conductivity the same as the conductivity of the source diffusion layer, and is formed outside and neighboring the body diffusion layer, and the diode element includes a vertical bipolar transistor including a collector diffusion layer that forms a collector of the diode element, a base diffusion layer that has a conductivity opposite to a conductivity of the collector diffusion layer, and forms a base of the diode element in the collector diffusion layer, said base being connected to the collector, and an emitter diffusion layer that has a conductivity the same as the conductivity of the collector diffusion layer, and forms an emitter of the diode element in the base diffusion layer, thereby producing a diode between the base and the emitter, and wherein a drain of the switching element and an anode of the diode element are connected to the switching terminal, and a cathode of the diode element is connected to the output terminal, wherein the diode element further includes a high concentration diffusion layer formed in the base diffusion layer in a direction intersecting a longitudinal direction of the base diffusion layer, and the high concentration diffusion layer has the same conductivity and a higher impurity concentration as compared to the base diffusion layer.