Process for the preparation of a semi-crystalline semi-aromatic polyamide copolymer (Co-PA) having a melting temperature (Tm-Co-PA) of at least 300°C, comprising steps of (a) preparing a first semi-crystalline semi-aromatic polyamide (A), having a melting temperature (Tm-A) of at least 310°C; and consisting of repeat units derived from ∘ 45 - 50 mol % terephthalic acid; ∘ 47.5 - 50 mol % of diamine; and ∘ 0 - 5 mol % of one or more other amine and/or acid group containing components; the mol % being relative to the total molar amount of said amine and/or acid group containing components; and wherein polyamide (A) is prepared by a process comprising direct solid-state polymerization of a diamine-dicarboxylic acid salt of the terephthalic acid and the diamine; (b) providing a polyamide (B), being ∘ an amorphous polyamide having a glass transition temperature (Tg-B) below Tm-A, or ∘ a second semi-crystalline polyamide having a melting temperature (Tm-B) below Tm-A, or ∘ a combination of the amorphous polyamide and the second semi-crystalline polyamide; (c) conducting a transamidation reaction between the polyamide (A) and the polyamide (B) by heating and melt-mixing polyamide (A) and polyamide (B), wherein the mean residence time of the melt in the melt-mixing step is 30 seconds or more, thereby obtaining a miscible polymer melt with a temperature (T-melt) above Tm-A; and (d) cooling the melt to a temperature below the solidification temperature of the melt, thereby obtaining a solid semi-crystalline semi-aromatic polyamide copolymer having a melting temperature Tm-Co-PA of at least 2.5°C below Tm-A, wherein the melting temperature is determined by DSC by the method according to ISO 11357-3 with a scan rate of 20 °C/min in the first heating cycle, and the glass transition temperature is measured by DSC by the method according to ISO-11357-2 with a heating rate of 20°C/minute in the second heating cycle. (a) preparing a first semi-crystalline semi-aromatic polyamide (A), having a melting temperature (Tm-A) of at least 310°C; and consisting of repeat units derived from ∘ 45 - 50 mol % terephthalic acid; ∘ 47.5 - 50 mol % of diamine; and ∘ 0 - 5 mol % of one or more other amine and/or acid group containing components; the mol % being relative to the total molar amount of said amine and/or acid group containing components; and wherein polyamide (A) is prepared by a process comprising direct solid-state polymerization of a diamine-dicarboxylic acid salt of the terephthalic acid and the diamine; ∘ 45 - 50 mol % terephthalic acid; ∘ 47.5 - 50 mol % of diamine; and ∘ 0 - 5 mol % of one or more other amine and/or acid group containing components; the mol % being relative to the total molar amount of said amine and/or acid group containing components; and (b) providing a polyamide (B), being ∘ an amorphous polyamide having a glass transition temperature (Tg-B) below Tm-A, or ∘ a second semi-crystalline polyamide having a melting temperature (Tm-B) below Tm-A, or ∘ a combination of the amorphous polyamide and the second semi-crystalline polyamide; ∘ an amorphous polyamide having a glass transition temperature (Tg-B) below Tm-A, or ∘ a second semi-crystalline polyamide having a melting temperature (Tm-B) below Tm-A, or ∘ a combination of the amorphous polyamide and the second semi-crystalline polyamide; (c) conducting a transamidation reaction between the polyamide (A) and the polyamide (B) by heating and melt-mixing polyamide (A) and polyamide (B), wherein the mean residence time of the melt in the melt-mixing step is 30 seconds or more, thereby obtaining a miscible polymer melt with a temperature (T-melt) above Tm-A; and (d) cooling the melt to a temperature below the solidification temperature of the melt, thereby obtaining a solid semi-crystalline semi-aromatic polyamide copolymer having a melting temperature Tm-Co-PA of at least 2.5°C below Tm-A, <EOS>