A semiconductor device comprising: at least a first switching circuit (T1, T2) and a second switching circuit (T5, T6) which switching circuits are connected in parallel, wherein each switching circuit comprising at least a first switching element (T1; T5) and a second switching element (T2; T6), which switching elements are IGBT chips, and which first and second switching elements are connected in series, a clamping diode connected to a node between the switching elements (T1, T2) of the first switching circuit (T1, T2), a clamping diode connected to a node between the switching elements (T5, T6) of the second switching circuit (T5, T6); a base potential line connecting auxiliary emitter terminals of the first switching elements (T1, T5) of the first and second switching circuit at a base potential (T1E) for applying an equivalent control signal on the first switching elements (T1, T5); and a wiring line that connects the node between the in series connected first switching element and second switching element of the first switching circuit (T1, T2) with the node between the in series connected first switching element and second switching element of the second switching circuit (T5, T6), which wiring line has a current carrying capacity approximately equal to a rated current of a semiconductor element of the first switching elements and a lower resistance value than the base potential line, wherein the wiring line has a resistance value not larger than 0.1 ohm, wherein the second switching element of the first switching circuit (T1, T2) and the second switching element of the second switching circuit (T5, T6) are respectively mounted on circuit patterns formed on individual adjacent insulated circuit boards (11, 12), and the wiring line connects the circuit patterns forming the nodes on the adjacent insulated circuit boards (11, 12), and wherein each of the adjacent insulated circuit boards (11, 12) comprises a part of the base potential line, and the parts of the base potential line on the adjacent insulated circuit boards (11, 12) are connected together with a bonding wire that composes a part of the base potential line. at least a first switching circuit (T1, T2) and a second switching circuit (T5, T6) which switching circuits are connected in parallel, wherein each switching circuit comprising at least a first switching element (T1; T5) and a second switching element (T2; T6), which switching elements are IGBT chips, and which first and second switching elements are connected in series, a clamping diode connected to a node between the switching elements (T1, T2) of the first switching circuit (T1, T2), a clamping diode connected to a node between the switching elements (T5, T6) of the second switching circuit (T5, T6); a base potential line connecting auxiliary emitter terminals of the first switching elements (T1, T5) of the first and second switching circuit at a base potential (T1E) for applying an equivalent control signal on the first switching elements (T1, T5); and a wiring line that connects the node between the in series connected first switching element and second switching element of the first switching circuit (T1, T2) with the node between the in series connected first switching element and second switching element of the second switching circuit (T5, T6), which wiring line has a current carrying capacity approximately equal to a rated current of a semiconductor element of the first switching elements and a lower resistance value than the base potential line, wherein the wiring line has a resistance value not larger than 0.1 ohm, wherein the second switching element of the first switching circuit (T1, T2) and the second switching element of the second switching circuit (T5, T6) are respectively mounted on circuit patterns formed on individual adjacent insulated circuit boards (11, 12), and the wiring line connects the circuit patterns forming the nodes on the adjacent insulated circuit boards (11, 12), and wherein each of the adjacent insulated circuit boards (11, 12) comprises a part of the base potential line, and the parts of the base potential line on the adjacent insulated circuit boards (11, 12) are connected together with a bonding wire that composes a part of the base potential line.