Abstract: An object of the present invention is to provide, even when a single crystal of a material other than AlN is used as a crystal, an AlN bulk single crystal having fewer defects and high quality, a method for producing such an AlN bulk single crystal, and a semiconductor device. A feature is to select, as a surface 1a of a hexagonal single crystal substrate serving as a seed crystal 1, a plane inclined at an angle of 10° to 80° with respect to the C-plane (FIG. 1(a)), and to grow an AlN single crystal 2 as a growth plane 2a on the surface 1a by a sublimation method (FIG. 1(b)).