Semiconductor device

A semiconductor device comprising:

• a semiconductor substrate of a first conductivity type;
• a first semiconductor layer of the first conductivity type formed on the semiconductor substrate and having a first conductivity type impurity concentration higher than a first conductivity type impurity concentration of the semiconductor substrate;
• a second semiconductor layer of a second conductivity type formed above the first semiconductor layer;
• a first device region formed in the second semiconductor layer and configured to operate based on a first reference voltage;
• a second device region formed in the second semiconductor layer and configured to operate based on a second reference voltage different from the first reference voltage, the second device region being spaced apart from the first device region;
• and
• a region isolation structure interposed between the first device region and the second device region and formed in a region extending from a front surface of the second semiconductor layer to the first semiconductor layer so as to electrically isolate the first device region and the second device region from each other.