A semiconductor device comprising: a lead frame on which a semiconductor element is mounted; an inner lead connected to an electrode of the semiconductor element ; and a first resin and a second resin that seal one portion of the lead frame , the semiconductor element , and the inner lead , wherein, when a face on a side of the lead frame on which the semiconductor element is mounted is assumed to be a mounting face and a face on a side opposite to that of the mounting face is assumed to be a heat dissipating face , a frame-form projection is provided in an outer peripheral end portion of the heat dissipating face , two opposing sides of the frame-form projection and a first thin molded portion that covers a region between the two sides are integrally molded using the second resin , two other opposing sides of the frame-form projection are molded using the first resin , wherein the second resin is a high heat dissipating resin whose thermal conductivity is higher than that of the first resin ; wherein an element sealing portion that covers one portion of the inner lead and the semiconductor element is molded on the mounting face using the first resin , characterized in that a second thin molded portion that covers one portion of a surface of the element sealing portion and the inner lead exposed in the element sealing portion is molded using the second resin ; wherein two sides of the frame-form projection molded using the first resin are covered with the second resin ; wherein the second resin covers the inner side faces of the two sides and faces parallel to the heat dissipating face . a lead frame on which a semiconductor element is mounted; an inner lead connected to an electrode of the semiconductor element ; and a first resin and a second resin that seal one portion of the lead frame , the semiconductor element , and the inner lead , wherein, when a face on a side of the lead frame on which the semiconductor element is mounted is assumed to be a mounting face and a face on a side opposite to that of the mounting face is assumed to be a heat dissipating face , a frame-form projection is provided in an outer peripheral end portion of the heat dissipating face , two opposing sides of the frame-form projection and a first thin molded portion that covers a region between the two sides are integrally molded using the second resin , two other opposing sides of the frame-form projection are molded using the first resin , wherein the second resin is a high heat dissipating resin whose thermal conductivity is higher than that of the first resin ; wherein an element sealing portion that covers one portion of the inner lead and the semiconductor element is molded on the mounting face using the first resin , characterized in that a second thin molded portion that covers one portion of a surface of the element sealing portion and the inner lead exposed in the element sealing portion is molded using the second resin ; wherein two sides of the frame-form projection molded using the first resin are covered with the second resin ; wherein the second resin covers the inner side faces of the two sides and faces parallel to the heat dissipating face . <EOS>