Measurements of electrical properties of ann‐type inversion layer at the surface of ap‐type InSb at low temperatures are reported. The surface inversion layer was produced by the application of the electric field normal to the surface of InSb in a metal‐oxide—p‐InSb structure. The observed field effect mobility shows that the motion of the electrons in the surface inversion layer is quantized in one direction and of two‐dimensional nature. Information for the trapping state in the oxide was obtained. A new type of current‐voltage characteristic, which is supposed to originate in the electron transfer from the lower quantum level to the higher one, was also observed.