A semiconductor device that has a source region, a channel region, and a drain region disposed in order from a surface of the semiconductor device in a thickness direction of a semiconductor substrate. The semiconductor device includes a gate insulating film having an extended portion that covers the surface of the semiconductor substrate outside of a gate trench and a top surface of a polysilicon gate. A connection gate trench branches from the gate trench, and joins a contact gate trench which is wider than the gate trench and the connection gate trench. The polysilicon gate is embedded in the connection gate trench and the contact gate, and extends from the gate trench to the contact gate trench through the connection gate trench. The gate contact groove is formed in the polysilicon gate within the contact gate trench.