Disclosed is a method for stripping a gallium nitride substrate, including: a gallium nitride substrate with a gallium nitride epitaxial structure directly grown on an upper surface thereof is acquired; an interior of the gallium nitride substrate is scanned and irradiated via the epitaxial structure by a laser beam, so as to generate a decomposition layer in the gallium nitride substrate, the laser beam being a laser having a pulse width on the order of less than 10−15 s, and a distance between the decomposition layer and the upper surface of the gallium nitride substrate being less than a thickness of the gallium nitride substrate; and the gallium nitride substrate is separated at the decomposition layer, so as to obtain a stripped gallium nitride substrate and a semiconductor device.