PURPOSE: To provide a long-life SiO2 electret.

CONSTITUTION: In the process for production of the electret in SiO2 including a first process of forming an SiO2 layer 10 on a solid substrate 5 by direct deposition in a vapor phase starting from a plasma contg. silicon and oxygen, the thus formed layer 10 is heat treated by raising its temp. to above 100°C for a time longer than one hour before being electrically charged. As a result, the electret increased in the expected life is produced.