Recently it was demonstrated that in atomic vapors weak control beams can manipulate (or switch) the propagation direction of strong light beams [Dawes et al., Science 308, 672 (2005)]. As a semiconductor analog of such all-optical switching, we present a proposal for similar manipulation and switching in planar semiconductor microcavities. Using a microscopic many-particle theory, we investigate the spatiotemporal dynamics of four-wave mixing signals and related instabilities in these systems. Even though the underlying physical processes are different from atomic systems, we find that microcavities allow for reversible directional manipulation of light. © 2009 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim.