Abstract: A furnace according to the present invention includes a rectangular chamber for receiving a semiconductor wafer or other body to be heated. The chamber has six plane reflecting walls. A bank of mutually parallel, equally spaced elongated heat radiation lamps extend between two opposite sidewalls inside the chamber. The distance between the outermost lamps and two opposite sidewalls extending at the sides of the lamps is less than one and one half times, and preferably equal to one half times, the spacing between adjacent lamps. The lamps are so arranged with respect to the walls that the configuration of lamps and their images formed by reflection approximate an array of infinite size which, at least in the plane of the lamps, is approximately continuous. A semiconductor body can be heated very rapidly and uniformly in this furnace, and as such, it is particularly suitable for rapidly annealing ion-implanted semiconductor wafers.