The semiconductor device includes a transistor including an oxide semiconductor film having a channel formation region, a gate insulating film, and a gate electrode layer. In the transistor, the channel length is small (5 nm or more and less than 60 nm, preferably 10 nm or more and 40 nm or less), and the thickness of the gate insulating film is large (equivalent oxide thickness which is obtained by converting into a thickness of silicon oxide containing nitrogen is 5 nm or more and 50 nm or less, preferably 10 nm or more and 40 nm or less). Alternatively, the channel length is small (5 nm or more and less than 60 nm, preferably 10 nm or more and 40 nm or less), and the resistivity of the source region and the drain region is 1.9×10−5 Ω·m or more and 4.8×10−3 Ω·m or less.