Threee new phases of the alloy Nb3Si have been produced by a relatively low‐temperature (∼800 °C) recrystallization anneal under pressures of up to 100 kbars. The new phases are apparently formed only when the Nb3Si starting material has a metastable body‐centered‐cubic structure which is prepared by sputtering. They are not formed when the Nb3Si starting material has the Ti3P‐type structure. One of the new high‐pressure phases has a superconducting transition temperatureTcof 5.45 K, but its crystal structure has not yet been identified. The phase formed at 60 and 100 kbars has a tetragonal Ni3P‐type structure, but the structure of the 80‐kbar phase is not known.