A semiconductor device comprising: a lead frame on which a semiconductor element is mounted; an inner lead (6, 11, 12) 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 (6, 11, 12), 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 (7a, 8a) is provided in an outer peripheral end portion of the heat dissipating face, two opposing sides of the frame-form projection (7a,8a) 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 (7a, 8a) 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 (6, 11, 12) 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 (6, 11, 12) exposed in the element sealing portion is molded using the second resin; wherein two sides of the frame-form projection (7a,8a) 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 (6, 11, 12) 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 (6, 11, 12), 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 (7a, 8a) is provided in an outer peripheral end portion of the heat dissipating face, two opposing sides of the frame-form projection (7a,8a) 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 (7a, 8a) 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 (6, 11, 12) 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 (6, 11, 12) exposed in the element sealing portion is molded using the second resin; wherein two sides of the frame-form projection (7a,8a) 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.