Provided is a semiconductor device, which prevents unnecessary voltage drop in a MOS transistor that is connected in series in a location between a booster circuit and a memory main body portion, to thereby operate on a low voltage and improve the ON/OFF ratio so that chip size shrinking and memory performance improvement are accomplished simultaneously. In a semiconductor memory device including a memory transistor portion and a select transistor portion, at least the select transistor portion is formed of a fin-shaped single-crystal semiconductor thin film.