In a semiconductor device, the marginal edge of a resist member on the side closer to a substrate is between first and third positions on a metal base plate. The third position is directly under an outer side surface of a metal plate. The first position is outside the third position and is away from a second position on the metal base plate directly under an outer side surface of the electrical insulating board, by a distance calculated by dividing “the height from a principal surface of the metal base plate to the front surface of the electrical insulating board” by “the tangent of the contact angle of solder created by the marginal edge stopping solder flow”. This makes it possible to ensure sufficient insulation distances between conductive patterns and the solder and to reduce creepage distances of the conductive patterns over the electrical insulating board.