The present invention relates to a magnesium oxide-based (MgO) inorganic coating intended to electrically insulate semiconductive substrates such as silicon carbide (SiC), and to a method for producing such an insulating coating. The method of the invention comprises the steps of preparing a treatment solution of at least one hydrolysable organomagnesium compound and/or of at least one hydrolysable magnesium salt, capable of forming a homogeneous polymer layer of magnesium oxyhydroxide by hydrolysis/condensation reaction with water; depositing the treatment solution of the hydrolysable organomagnesium compound or of the hydrolysable magnesium salt, onto a surface to form a magnesium oxide-based layer; and densifying the layer formed at a temperature of less than or equal to 1000° C.