An electronic device includes a pair of members which are connected to each other by a connecting portion layer interposed between connecting portions respectively formed thereon and which have thermal expansion coefficients different from each other. The connection layer is formed by diffusion reaction between the metal layers by which the metal layers are melted only in the vicinity of a contact interface between the layers, the metal layers being formed on the connecting portions with materials different from each other. At least one of the metal layers is formed by plating, thereby the connection layer is formed in a thickness sufficient to absorb differences in thermal expansion coefficients between the pair of members. Since melting temperature of the connection layer after the pair of members have been connected to each other is increased compared with melting temperature of each of the members in the diffusion reaction, the connection layer is prevented from being damaged due to heating treatment performed after the connection has been made, consequently excellent reliability of the electronic device is secured.