Amorphous alloys have been shown, at high pressure and high temperature, to transform into dense crystalline phases which are not found at ambient pressure. This behavior has been used to synthesize the Al5-Nb//3Si compound from amorphous sputter deposits employing a multi-anvil apparatus. X-ray diffraction examination has shown that the compound is produced in Nb-23. 7 at% Si alloy in an almost single-phased state with a high degree of atomic ordering. It is a superconductor with a sharp transition. The method can be applied to any system and proves to be a promising method of synthesis of new crystalline phases.