A semiaromatic polyester, characterized in that, the semiaromatic polyester comprises derivatives formed by the following components: a first component A, based on a total molar amount of the first component A, comprising: a1) from 40 to 60 mol% of at least one aliphatic dicarboxylic acid or ester derivatives thereof or anhydride derivatives thereof, a2) from 40 to 60 mol% of at least one aromatic dicarboxylic acid or ester derivatives thereof or anhydride derivatives thereof, a3) from 0 to 5 mol% of a compound containing sulfonate groups; a second component B with at least equimolar amount with respect to the first component A, comprising diols having from 2 to 12 carbon atoms; and a third component C, based on a total molar amount of the first component A, being one or more selected from the following: c1) from 0 to 5 mol% of a compound containing at least 3 hydroxy groups, c2) from 0 to 5 mol% of a dihydroxy compound containing an ether group, c3) from 0 to 25 mol% of a hydroxycarboxylic acid or cyclic derivatives thereof, and c4) from 0 to 25 mol% of an amino alkanol having from 2 to 12 carbon atoms, or an amino cycloalkanol having from 2 to 12 carbon atoms, c5) from 0 to 25 mol% of a diamine having from 1 to 12 carbon atoms, and c6) from 0 to 15 mol% of an aminocarboxylic acid compound, wherein the percentage of at least one of components c1) to c6) is not 0, and a total of the molar percentages of c1) to c6) is 100%; wherein the average segment length of a repeating unit Ba2 derived from the second component B and the component a2 of the semiaromatic polyester, is from 1.85 to 2.25 as calculated using 1 HNMR; and the carboxyl group content of the semiaromatic polyester is from 5 to 60 mmol/kg. a first component A, based on a total molar amount of the first component A, comprising: a1) from 40 to 60 mol% of at least one aliphatic dicarboxylic acid or ester derivatives thereof or anhydride derivatives thereof, a2) from 40 to 60 mol% of at least one aromatic dicarboxylic acid or ester derivatives thereof or anhydride derivatives thereof, a3) from 0 to 5 mol% of a compound containing sulfonate groups; a1) from 40 to 60 mol% of at least one aliphatic dicarboxylic acid or ester derivatives thereof or anhydride derivatives thereof, a2) from 40 to 60 mol% of at least one aromatic dicarboxylic acid or ester derivatives thereof or anhydride derivatives thereof, a3) from 0 to 5 mol% of a compound containing sulfonate groups; a second component B with at least equimolar amount with respect to the first component A, comprising diols having from 2 to 12 carbon atoms; and a third component C, based on a total molar amount of the first component A, being one or more selected from the following: c1) from 0 to 5 mol% of a compound containing at least 3 hydroxy groups, c2) from 0 to 5 mol% of a dihydroxy compound containing an ether group, c3) from 0 to 25 mol% of a hydroxycarboxylic acid or cyclic derivatives thereof, and c4) from 0 to 25 mol% of an amino alkanol having from 2 to 12 carbon atoms, or an amino cycloalkanol having from 2 to 12 carbon atoms, c5) from 0 to 25 mol% of a diamine having from 1 to 12 carbon atoms, and c6) from 0 to 15 mol% of an aminocarboxylic acid compound, c1) from 0 to 5 mol% of a compound containing at least 3 hydroxy groups, c2) from 0 to 5 mol% of a dihydroxy compound containing an ether group, c3) from 0 to 25 mol% of a hydroxycarboxylic acid or cyclic derivatives thereof, and c4) from 0 to 25 mol% of an amino alkanol having from 2 to 12 carbon atoms, or an amino cycloalkanol having from 2 to 12 carbon atoms, c5) from 0 to 25 mol% of a diamine having from 1 to 12 carbon atoms, and c6) from 0 to 15 mol% of an aminocarboxylic acid compound, wherein the percentage of at least one of components c1) to c6) is not 0, and a total of the molar percentages of c1) to c6) is 100%; wherein the average segment length of a repeating unit Ba2 derived from the second component B and the component a2 of the semiaromatic polyester, is from 1.85 to 2.25 as calculated using 1 HNMR; and the carboxyl group content of the semiaromatic polyester is from 5 to 60 mmol/kg.