In a manufacturing method for a semiconductor device according to an embodiment, a first heat treatment to anneal or oxidize an SiC layer in an atmosphere where a gas including carbon (C) exists is applied. Further, the semiconductor device according to the embodiment includes: an SiC substrate having a first surface and a second surface; a first conductivity type SiC layer disposed on the first surface side of the SiC substrate, and including a low level density region having Z1/2 level density of 1×1011 cm−3 or less measured by deep level transient spectroscopy (DLTS); a second conductivity type SiC region disposed on a surface of the SiC layer; a first electrode disposed on the SiC region; and a second electrode disposed on the second surface side of the SiC substrate.