PURPOSE: To form a superconductive oxide layer having a high Tc with the precise control of stoichiometric ratio and a temp. by repeating the application of a uniform solution of an organometallic compound of at least Bi and Cu on a substrate and the thermal decomposition to make it into a prescribed thickness.

CONSTITUTION: An organic solvent solution such as a hydrocarbon solution of carboxylate of Ca, Sr, Bi or Cu, e.g. calcium naphthenate, strontium octanate, bismuth octanate and copper 2-ethyl hexanate is deposited on the substrate of MgO, SrTiO3, Al2O3, ZrO2 or the like and the organic compound is thermally decomposed at 300-600°C. A superconductive oxide layer is obtained by repeating the operation up to reach a prescribed thickness and after that, firing it at 700-950°C. The layer having a ≥100 K critical temp. is produced by the method.