A miniaturized semiconductor device including a transistor in which a channel formation region is formed using an oxide semiconductor film and variation in electric characteristics due to a short-channel effect is suppressed is provided. In addition, a semiconductor device whose on-state current is improved is provided. A semiconductor device is provided with an oxide semiconductor film including a pair of second oxide semiconductor regions which are amorphous regions and a first oxide semiconductor region located between the pair of second oxide semiconductor regions, a gate insulating film, and a gate electrode provided over the first oxide semiconductor region with the gate insulating film interposed therebetween. One or more kinds of elements selected from Group 15 elements such as nitrogen, phosphorus, and arsenic are added to the second oxide semiconductor regions.