A semiconductor device comprising: a first circuit board including a first principal surface mounted with a plurality of semiconductor elements constituting a main circuit; a second circuit board including a second principal surface mounted with a plurality of electronic components and being arranged such that a back surface of the second principal surface opposes the first principal surface; a plurality of connecting terminals (4, 5, 6, 7, 8) securely connected to the first circuit board; and a case covering the first circuit board and the second circuit board, wherein each of the connecting terminals (4, 5, 6, 7, 8) includes an external terminal connecting portion (30, 40), having an end surface (30a, 40a) to connect an external terminal thereto and located at the second principal surface side of the second circuit board faces, and a substrate-fixed portion (31, 41) securely connected to the first circuit board, the external terminal connecting portion (30, 40) and the substrate-fixed portion (31, 41) being eccentrically located when viewed from a direction in which the first circuit board and the second circuit board are opposed, a hole is provided in the case to allow the end surface (30a, 40a) of the external terminal connecting portion (30, 40) to be exposed therethrough, a seal attachment portion (35, 43) is provided on a portion of the external terminal connecting portion (30, 40) including the end surface (30a, 40a) to attach thereto a seal member to seal a gap between the portion and the case, at least one of the connecting terminals (4, 5, 6, 7, 8) includes a reduced sectional area portion having a sectional area smaller than an area of the top end surface (30a, 40a) in a region facing the plurality of electronic components arranged on the second circuit board on the external terminal connecting portion (30, 40), and the reduced sectional area portion is provided in a region from the seal attachment portion (35, 43) to an end in an opposite side of the end surface (30a, 40a), characterized in that a rim of the top end surface (30a, 40a) of the external terminal connecting portion (30, 40) has a plurality of straight regions and a shape of the hole corresponds to a shape of the top end surface (30a, 40a). a first circuit board including a first principal surface mounted with a plurality of semiconductor elements constituting a main circuit; a second circuit board including a second principal surface mounted with a plurality of electronic components and being arranged such that a back surface of the second principal surface opposes the first principal surface; a plurality of connecting terminals (4, 5, 6, 7, 8) securely connected to the first circuit board; and a case covering the first circuit board and the second circuit board, wherein each of the connecting terminals (4, 5, 6, 7, 8) includes an external terminal connecting portion (30, 40), having an end surface (30a, 40a) to connect an external terminal thereto and located at the second principal surface side of the second circuit board faces, and a substrate-fixed portion (31, 41) securely connected to the first circuit board, the external terminal connecting portion (30, 40) and the substrate-fixed portion (31, 41) being eccentrically located when viewed from a direction in which the first circuit board and the second circuit board are opposed, a hole is provided in the case to allow the end surface (30a, 40a) of the external terminal connecting portion (30, 40) to be exposed therethrough, a seal attachment portion (35, 43) is provided on a portion of the external terminal connecting portion (30, 40) including the end surface (30a, 40a) to attach thereto a seal member to seal a gap between the portion and the case, at least one of the connecting terminals (4, 5, 6, 7, 8) includes a reduced sectional area portion having a sectional area smaller than an area of the top end surface (30a, 40a) in a region facing the plurality of electronic components arranged on the second circuit board on the external terminal connecting portion (30, 40), and the reduced sectional area portion is provided in a region from the seal attachment portion (35, 43) to an end in an opposite side of the end surface (30a, 40a), characterized in that a rim of the top end surface (30a, 40a) of the external terminal connecting portion (30, 40) has a plurality of straight regions and a shape of the hole corresponds to a shape of the top end surface (30a, 40a).