A method by which generation of leak current can be suppressed and also a fine element can be formed by performing element isolation at a temperature at which a glass substrate can be used is provided. The method includes a first step of forming a base film over a glass substrate; a second step of forming a semiconductor film over the base film; a third step of forming, over the semiconductor film, a film preventing oxidation or nitridation of the semiconductor film into a predetermined pattern; and a fourth step of performing element isolation by radical oxidation or radical nitridation of a region of the semiconductor film, which is not covered with the predetermined pattern, at a temperature of the glass substrate lower than a strain point thereof by 100.degree. C. or more, where radical oxidation or radical nitridation is performed over a semiconductor film placed apart from a plasma generation region, in a plasma treatment chamber with an electron temperature within the range of 0.5 to 1.5 eV, preferably less than or equal to 1.0 eV, and an electron density within the range of 1.times.10.sup.11cm.sup.-3 to 1.times.10.sup.13cm.sup.-3.