In a method for manufacturing a semiconductor device, the method includes the step of growing a nitride-based III-V compound semiconductor layer, which forms a device structure, directly on a substrate without growing a buffer layer, the substrate being made of a material with a hexagonal crystal structure and having a principal surface that is oriented off at an angle of not less than −0.5° and not more than 0° from an R-plane with respect to a direction of a C-axis.