Abstract: The present invention is directed to a method for isothermally thermoforming a thermoplastic composite, which composite comprises a matrix and a reinforcement, both issued of a semi-crystalline polymer of the same class, comprising the steps of: i) placing a stack of said thermoplastic composite, having a temperature below the sealing or melting point of said matrix, in a mould;, which mould has a temperature between the sealing or melting point of said matrix and the melting point of said reinforcement; ii) closing said mould; and iii) opening the mould after a dwell time; wherein the temperature of said mould is between the sealing point of said matrix and the melting point of said reinforcement, at least for a period of time after step ii).