Abstract: For joining shaped bodies of silicon nitride together, silicon nitride surfaces to be joined are first polished and then put into an apparatus for applying sputtered layers where they are first cleaned by ion bombardment in argon, followed immediately by sputtering with silicon in a nitrogen atmosphere such that a layer is deposited having a nitrogen content exceeding the Si.sub.3 N.sub.4 stoichiometric ratio. This readily provides a layer of the composition Si.sub.3 N.sub.5.5. A complementary nitrogen deficient layer is also provided in the joint before hot pressing, either in the form of a silicon layer that goes between the nitrogen-rich silicon nitride layers or in the form of a nitrogen-deficient silicon nitride layer sputtered onto a polished silicon nitride surface at relatively low nitrogen pressure. The parts are isostatically hot pressed together at 1500.degree. to 1750.degree. C. in a nitrogen atmosphere. The layers which are usually thinner than 1 .mu.