Abstract: A new method for the highly stereoselec- tive cis-semihydrogenation of internal alkynes is de- scribed based on in situ generated Ni(0) nanoparti- cles and molecular hydrogen. This reduction system also allows the semihydrogenation of terminal al- kynes. ... Keywords: (Z)-alkenes; alkynes; cis-hydrogenation; nanoparticles; nickel; stereoselectivity ... The semihydrogenation of the carbon-carbon triple bond is a particularly valuable reaction in synthetic or- ganic ...