A monocrystalline superalloy with a nickel based matrix and particularly intended for the manufacture of turbine blades, has the following composition, by weight: Al=5.4% to 6.2%; Co=4% to 7%; Cr=6% to 9%; Mo=0% to 2.5%; Ta=5.5% to 8%; Ti=O% to 1%; W=7% to 9%; and Ni=balance to 100%.The invention also provides a method of improving the alloy's resistance to creep, in which the Ni.sub.3 Al type .gamma.' phase is put completely into solution at a first temperature, and then the .gamma.' phase is precipitated into the .gamma. solid solution at a temperature greater than 1000.degree. C. This treatment considerably increases the alloy's resistance to creep over a wide range of temperatures.