A semiconductor module comprising: a substrate formed of a metal; an insulating layer formed on the substrate; a plurality of wiring patterns (33a, 33b, 33c, 33d) formed on the insulating layer; a bare-chip transistor mounted on one of the plurality of wiring patterns (33a, 33b, 33c, 33d) via a solder; and a copper connector (36a, 36b) formed of a copper plate and connecting an electrode formed on a top surface of the bare-chip transistor and another one of the plurality of wiring patterns (33a, 33b, 33c, 33d) via a solder, wherein the copper connector (36a, 36b) includes a flat portion (36aa, 36ba), a first leg portion (36ab, 36bb) folded downward extending from one end of the flat portion (36aa, 36ba) and bonded to the electrode, and a second leg portion (36ac, 36bc) folded downward extending from the other end of the flat portion (36aa, 36ba) and bonded to the another one of the plurality of wiring patterns (33a, 33b, 33c, 33d) to form a bridge shape, and wherein the first leg portion (36ab, 36bb) comprises a width-reduced portion folded downward extending from the one end of the flat portion (36aa, 36ba) to have a taper shape gradually decreasing a width of the width-reduced portion from the one end of the flat portion (36aa, 36ba), and a stress-reducing portion having a shape for reducing stress acting on the bonding face is formed on the bonding face of the first leg portion (36ab, 36bb) bonded to the electrode, wherein a notch portion is formed as the stress-reducing portion in the bonding face, or the bonding face is formed to have a small thickness, as the stress-reducing portion, or a chamfered portion is formed as the stress-reducing portion at a corner of the bonding face, or a hole is formed as the stress-reducing portion at the center of the bonding face, wherein notches are formed in the width-reduced portion on both sides in a width direction of the first leg portion (36ab, 36bb), so as to face each other, and notches are formed on both sides in a width direction of the second leg portion (36ac, 36bc), so as to face each other, each of the notches having a semi-circular shape, wherein the notches form a dumbbell portion having a dumbbell shape for reducing the stress acting on the bonding face in each of the first leg portion (36ab, 36bb) and the second leg portion (36ac, 36bc). a substrate formed of a metal; an insulating layer formed on the substrate; a plurality of wiring patterns (33a, 33b, 33c, 33d) formed on the insulating layer; a bare-chip transistor mounted on one of the plurality of wiring patterns (33a, 33b, 33c, 33d) via a solder; and a copper connector (36a, 36b) formed of a copper plate and connecting an electrode formed on a top surface of the bare-chip transistor and another one of the plurality of wiring patterns (33a, 33b, 33c, 33d) via a solder, wherein the copper connector (36a, 36b) includes a flat portion (36aa, 36ba), a first leg portion (36ab, 36bb) folded downward extending from one end of the flat portion (36aa, 36ba) and bonded to the electrode, and a second leg portion (36ac, 36bc) folded downward extending from the other end of the flat portion (36aa, 36ba) and bonded to the another one of the plurality of wiring patterns (33a, 33b, 33c, 33d) to form a bridge shape, and wherein the first leg portion (36ab, 36bb) comprises a width-reduced portion folded downward extending from the one end of the flat portion (36aa, 36ba) to have a taper shape gradually decreasing a width of the width-reduced portion from the one end of the flat portion (36aa, 36ba), and a stress-reducing portion having a shape for reducing stress acting on the bonding face is formed on the bonding face of the first leg portion (36ab, 36bb) bonded to the electrode,