To provide a small and high-performance semiconductor device.

The semiconductor device includes a first GaN layer 12 formed on an SiC substrate 11, a source pad 23 formed on the first GaN layer 12, a plurality of columnar GaN layers 14 formed on the first GaN layer 12, a second GaN layer 16 formed so as to be in contact with upper ends of these columnar GaN layers 14, and a drain pad 25 formed on the second GaN layer 16. Each of the plurality of columnar GaN layers 14 includes a source region 18, a gate region 19, and a drain region 17 having a smaller diameter than the source region formed sequentially from the bottom. A first insulating film 20 is formed around the gate region 18. A gate electrode 21 is formed around the gate region 19. A second insulating film 22 is formed around the drain region 17 via a predetermined space.