There is provided a semiconductor device including DTMOS and a substrate variable-bias transistor and a portable electronic device both operable with reduced power consumption. N-type deep well regions (12) are formed in one P-type semiconductor substrate (11). The N-type deep well regions (12, 12) are electrically isolated by the P-type semiconductor substrate (11). Over the N-type deep well regions (12), a P-type deep well region (13) and a P-type shallow well region (15) are formed to fabricate an N-type substrate variable-bias transistor (26). Over the N-type deep well region (12), an N-type shallow well region (14) is formed to fabricate a P-type substrate variable-bias transistor (25). Further a P-type DTMOS (28) and an N-type DTMOD (27) are fabricated.