In a semiconductor device cooling apparatus which cools a semiconductor device uniformly with a simple structure, a coolant is supplied from a supply port to the center of a heat transmission plate on which a semiconductor device is disposed in intimate contact therewith, is radially flown toward the peripheral edge portion of the heat transmission plate through a gap-shaped flow path which is formed by a gap forming plate composed of two thin plate members of a gap interval plate acting as a spacer and a gap top plate disposed on the gap interval plate and has a small height, is collected by a collection groove formed around the peripheral edge portion, and is discharged from a discharge port.