The present invention provides: an insulating substrate or metal-clad laminate able to sufficiently reduce or prevent negative warping of a semiconductor device; a printed wiring board that uses the insulating substrate or metal-clad laminate; and a semiconductor device. The insulating substrate comprises the cured product of a laminate that includes at least one fibrous base material layer and at least two resin layers, the outermost layer on both surfaces being a resin layer. At least one of the fibrous base material layers is lateralized towards the first surface side or the reverse surface thereof, which is the second surface side, with respect to a baseline position, namely the splitting position when the thickness of each region resulting from evenly splitting the overall thickness of the insulating substrate by the number of fibrous base material layers is further evenly split in two. It is possible to produce a printed wiring board by using, as a core substrate, a metal-clad laminate containing the insulating substrate. Also, it is possible to produce a semiconductor device by mounting a semiconductor element onto the printed wiring board.