To solve the problem that the characteristic required in the device forming on the surface or growth of a single crystal film can not be obtained because the crystal surface is not obtained, in the material where the crystal surface cannot sufficiently be obtained by the thermal, chemical and mechanical surface treatment.

In this super-smooth crystal face forming method for a single crystal substrate, a single crystal substrate consisting of SiC, nitrides and oxides of group III or a dielectric body to be polished derivative with a rotary buff polishing method or an ultrasonic vibration polishing method, by using an alkaline aqueous polishing liquid adjusted to pH7 to 10, containing 5 to 40 wt.% of colloidal silica to water to peel off the defective layer whose crystallinity of the surface part is not single crystal, to form a super smooth crystal face consisting of the interface of a crystalline part and a defective layer part.