A high-voltage transistor and a peripheral circuit including a second conductivity type MOSFET are provided together on a first conductivity type semiconductor substrate. The high-voltage transistor includes: a low concentration drain region of a second conductivity type formed in the semiconductor substrate; a low concentration source region of a second conductivity type formed in the semiconductor substrate and spaced apart from the low concentration drain region; and a high concentration source region of a second conductivity type having a diffusion depth deeper than that of the low concentration source region. A diffusion depth of the low concentration source region is equal to that of source/drain regions of the MOSFET.