To divide a β-type gallium oxide substrate having a (001) plane as a main surface satisfactorily. A method of diving a gallium oxide substrate includes: a step of forming a plurality of dividing grooves 13 along the extending direction of the (100) plane of a β-type gallium oxide substrate 10 having the (001) plane as the main surface; a step of processing the β-type gallium oxide substrate 10 into strips by cutting the substrate 10 in a direction perpendicular to the extending direction of the dividing grooves 13; and a step of cleaving the strip-shaped β-type gallium oxide substrates 10 along the dividing grooves 13 for singulation. Since the plurality of dividing grooves 13 are thus formed along the cleavage planes, the substrate can be divided satisfactorily without causing flaky peeling on the cleavage surfaces by cleaving the substrate along the dividing grooves 13.