PURPOSE: To form a Bi-Sr-Ca-Cu-O superconducting thin film of (2212) phase by molecular-beam epitaxy.

CONSTITUTION: NO2 gas 14 is supplied on the film forming surface 38 of a heated MgO (100) substrate 30, and the molecular beams of the elements 28 of Bi, Sr, Ca and Cu are supplied to form a superconducting film. In this case, the substrate heating temp. is controlled to 600-750°C, e.g. 700°C, the supply of NO2 gas to the film forming surface to 1×1017-1×1018 atoms/s cm2, e.g. 1×1017 atoms/s cm2, and the molecular beam intensity ratio of the Bi, Sr, Ca and Cu on the film forming surface to about 2:2:1:1. For example, the molecular beam intensities of Bi, Sr, Ca and Cu are respectively controlled to 4.9×1014, 5.1×1014, 2.3×1014 and 2.3×1014 atoms/s cm2, and the film forming rate is adjusted to ≤2×10-8cm/s, e.g. 2×10-8cm/s.