A prepreg that yields a semiconductor device which, even when using Cu wire, exhibits excellent reliability under conditions of high temperature and high humidity (heat-resistant and moisture-resistant reliability), a metal-clad laminate and a printed wiring board that use the prepreg, and a semiconductor device that uses the printed wiring board. Specifically disclosed are a prepreg comprising a substrate and a B-staged resin composition comprising (a) a thermosetting resin, (b) a hydrotalcite compound having a specific composition, (c) zinc molybdate, and (d) lanthanum oxide.