A semiconductor device comprising: a semiconductor chip (7,8;30,31); a first conductive member (6;29) for supporting the semiconductor chip; a second conductive member arranged above the semiconductor chip, facing the first conductive member spaced apart therefrom, a resin package that seals the semiconductor chip, the first conductive member and the second conductive member so as to get into a space between the first conductive member and the second conductive member, such that a portion of the resin package is sandwiched between the first conductive member and the second conductive member to thus allow the portion to be held therebetween; a joint material (23;45) provided between the first conductive member and the semiconductor chip; a plurality of release grooves (13;36) formed on the surface of the first conductive member and arranged away from the semiconductor chip, wherein each of the release grooves has one end and another end, wherein the one end and the other end of each of the release grooves are connected to opposite peripheral edges of the first conductive member, respectively, the first conductive member has end surfaces forming the peripheral edges, and the one end and the other end of the release grooves are opened at the end surfaces, respectively; a stepped structure being formed on the lateral surface of the each of the release grooves, the stepped structure being formed by partitioning the release grooves into a plurality of stages in the depth direction, the stepped structure extending from the one end to the other end of each of the release grooves; the semiconductor chip is arranged in a chip area sandwiched between adjacent release grooves; wherein the semiconductor device is a power semiconductor module including: a high-side assembly, which includes a high-side heat-dissipation block as the first conductive member and a high-side Insulated Gate Bipolar transistor (IGBT) as the semiconductor chip arranged on the high-side heat-dissipation block; a low-side assembly, which is arranged away from the high-side assembly and includes a low-side heat dissipation block as another first conductive member and a low-side IGBT as another semiconductor chip arranged on the low-side heat dissipation block; and wherein the resin package seals the high-side assembly and the low-side assembly; and wherein a relay terminal as the second conductive member is arranged above the high-side IGBT and is electrically connected to the low-side heat dissipation block. a semiconductor chip (7,8;30,31); a first conductive member (6;29) for supporting the semiconductor chip; a second conductive member arranged above the semiconductor chip, facing the first conductive member spaced apart therefrom, a resin package that seals the semiconductor chip, the first conductive member and the second conductive member so as to get into a space between the first conductive member and the second conductive member, such that a portion of the resin package is sandwiched between the first conductive member and the second conductive member to thus allow the portion to be held therebetween; a joint material (23;45) provided between the first conductive member and the semiconductor chip; a plurality of release grooves (13;36) formed on the surface of the first conductive member and arranged away from the semiconductor chip, wherein each of the release grooves has one end and another end, wherein the one end and the other end of each of the release grooves are connected to opposite peripheral edges of the first conductive member, respectively, the first conductive member has end surfaces forming the peripheral edges, and the one end and the other end of the release grooves are opened at the end surfaces, respectively; a stepped structure being formed on the lateral surface of the each of the release grooves, the stepped structure being formed by partitioning the release grooves into a plurality of stages in the depth direction, the stepped structure extending from the one end to the other end of each of the release grooves; the semiconductor chip is arranged in a chip area sandwiched between adjacent release grooves; wherein the semiconductor device is a power semiconductor module including: a high-side assembly, which includes a high-side heat-dissipation block as the first conductive member and a high-side Insulated Gate Bipolar transistor (IGBT) as the semiconductor chip arranged on the high-side heat-dissipation block; a low-side assembly, which is arranged away from the high-side assembly and includes a low-side heat dissipation block as another first conductive member and a low-side IGBT as another semiconductor chip arranged on the low-side heat dissipation block; and a high-side assembly, which includes a high-side heat-dissipation block as the first conductive member and a high-side Insulated Gate Bipolar transistor (IGBT) as the semiconductor chip arranged on the high-side heat-dissipation block; a low-side assembly, which is arranged away from the high-side assembly and includes a low-side heat dissipation block as another first conductive member and a low-side IGBT as another semiconductor chip arranged on the low-side heat dissipation block; and wherein the resin package seals the high-side assembly and the low-side assembly; and wherein a relay terminal as the second conductive member is arranged above the high-side IGBT and is electrically connected to the low-side heat dissipation block.