Semiconductor device and manufacturing method of the same

A method for manufacturing a semiconductor device including a variable capacitor and a bipolar transistor on a common semiconductor substrate, comprising the steps of:

• (a) forming a first semiconductor layer of a first conductivity type in a region of the semiconductor substrate where the variable capacitor is to be formed, and forming a second semiconductor layer of the first conductivity type in a region of the semiconductor substrate where the bipolar transistor is to be formed;
• and
• (b) after the step (a), forming a third semiconductor layer on the first semiconductor layer of the semiconductor substrate and forming a fourth semiconductor layer on the second semiconductor layer both by an epitaxial growth method.