A brief review is given of experiments on semiconductors at high pressure, using the diamond-anvil cell. Experimental techniques are discussed first, with emphasis on the reasons why they have revolutionized high-pressure science. Then, examples of experimental results are given, including X-ray diffraction (equation of state, structural phase transitions, metastable phases), Raman and Brillouin spectroscopy (lattice-mode frequencies), photoluminescence spectroscopy (electronic and defect energies), resistivity and galvanomagnetic effects (scattering mechanisms and electronic transitions). These examples are taken from Si, GaAs, InP and solid H2.