In one embodiment, a semiconductor device includes a semiconductor substrate, and first and second transistors of first and second conductivity types on the substrate. The first transistor includes a first gate electrode on the substrate, a first source region of the second conductivity type and a first drain region of the first conductivity type disposed to sandwich the first gate electrode, and a first channel region of the first or second conductivity type disposed between the first source region and the first drain region. The second transistor includes a second gate electrode on the substrate, a second source region of the first conductivity type and a second drain region of the second conductivity type disposed to sandwich the second gate electrode, and a second channel region disposed between the second source region and the second drain region and having the same conductivity type as the first channel region.