Polymer film made of a polyamide composition comprising at least 80 weight percentage (wt.%) of a semi-crystalline semi-aromatic polyamide with a melting temperature (Tm) in the range of 290-340°C, wherein the wt.% is relative to the total weight of the polymer composition, wherein the polymer film has an thermal expansion coefficient in the temperature range of 20°C - Tg, measured in plane with the method according to ASTM D969-08, of 10 - 40 ppm/K and is prepared by a process comprising steps wherein first the polyamide composition is melt processed, the melt is cast into a film, the film is biaxially stretched and the biaxially stretched film is heat set the process comprising steps wherein i. a polymer moulding composition comprising at least 80 wt.% relative to the total weight of the polymer composition of a semi-crystalline semi-aromatic polyamide having a melting temperature (Tm) in the range of 290-340°C and a glass transition temperature (Tg) is melt processed at a temperature above Tm, thereby forming a polymer melt; ii. the polymer melt obtained in step 1 is extruded into a film and the film is cast and immediately cooled to a temperature below the glass transition temperature; iii. the casted film obtained in step 2 is biaxially stretched at a temperature close to the glass transition temperature; and iv. the biaxially stretched film obtained in step 3 is heat set at a temperature between the glass transition temperature and the melting temperature; and during which steps the following conditions have been applied: i. during the melt processing the polymer composition is kept above the melting temperature of the semi-crystalline semi-aromatic polyamide for a residence time of at most 1 minute; ii. during the casting the film is casted on a surface with a surface temperature of at least 25 °C below Tg; iii. during the biaxial stretching, the casted film is biaxially stretched by a factor of at least 2x2 at a temperature in the range from Tg- 5°C up to and including Tg + 20°C; and iv. during the heat setting, the biaxially stretched film is kept at a temperature in the range from Tm- 80°C up to and including Tm-10°C, preferably in the range from Tm- 60°C up to and including Tm-25°C. i. a polymer moulding composition comprising at least 80 wt.% relative to the total weight of the polymer composition of a semi-crystalline semi-aromatic polyamide having a melting temperature (Tm) in the range of 290-340°C and a glass transition temperature (Tg) is melt processed at a temperature above Tm, thereby forming a polymer melt; ii. the polymer melt obtained in step 1 is extruded into a film and the film is cast and immediately cooled to a temperature below the glass transition temperature; iii. the casted film obtained in step 2 is biaxially stretched at a temperature close to the glass transition temperature; and iv. the biaxially stretched film obtained in step 3 is heat set at a temperature between the glass transition temperature and the melting temperature; i. during the melt processing the polymer composition is kept above the melting temperature of the semi-crystalline semi-aromatic polyamide for a residence time of at most 1 minute; ii. during the casting the film is casted on a surface with a surface temperature of at least 25 °C below Tg; iii. during the biaxial stretching, the casted film is biaxially stretched by a factor of at least 2x2 at a temperature in the range from Tg- 5°C up to and including Tg + 20°C; and iv. during the heat setting, the biaxially stretched film is kept at a temperature in the range from Tm- 80°C up to and including Tm-10°C, preferably in the range from Tm- 60°C up to and including Tm-25°C.