Abstract: Fabrication of the polymer-based composites with excellent high temperature resistance and thermal conductivity is very important for the packaging protection, efficient heat dissipation and processing of electronic components. In this work, high temperature resistant and thermally conductive hexagonal boron nitride (BN)/semi-aromatic polyamide 12T (PA12T) composites with uniform dispersion and orientation filler structure were prepared by mixed solvent dispersion (MSD) method, and the microstructure, thermal conductivity, high-temperature resistance, dielectric and mechanical properties of the composites were systematically characterized. The results show that the BN powder and PA12T powder can be suspended uniformly in the mixed solvent. Next, combining the vacuum-assisted self-assembly technique and vacuum hot compression method, the composites with uniformly dispersed and oriented BN structure are fabricated successfully. When the content of BN is 40wt% in BN/PA12T composite, the in-plane thermal conductivity of the composite prepared by the MSD method is 2.73 W/(m·K), which is 1.72 times that of the composite (1.59 W/(m·K)) prepared by the mechanical mixing (MM) method. Furthermore, the composite prepared by the MSD method also possesses excellent mechanical properties, low dielectric permittivity of 3.6 and dielectric loss of 0.016, outstanding high-temperature resistance with the initial decomposition temperature of 446℃ and Vicat softening temperature of more than 250℃. Therefore, the BN/PA12T composite prepared by the MSD method will have a wide range of applications in the fields of electronic packaging and thermal management.