Wafers of semi-conducting material are formed by moulding and directional crystallization from a liquid mass of this material. A seed, situated at the bottom of the crucible, presents an orientation along non-dense crystallographic planes. The mould is filled with the molten semi-conducting material by means of a piston or by creation of a pressure difference in the device. The mould is preferably coated with a non-wettable anti-adhesive deposit.