An idea of applying a film of high-k (HK) material to the trench lateral double-diffused MOSFET (LDMOS) is proposed and studied by simulation. Through introducing an HK film around the SiO2 trench, the flow of electric flux is guided, and the distribution of the surface electric field is modulated. As a result, the tradeoff relationship between breakdown voltage (BV) and specific $ \mathrm{\scriptscriptstyle ON}$ -resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}})$ is improved. Simulation results indicate that the HK film with a permittivity of 475 and a thickness of 400 nm can effectively reduce ${R}_{ \mathrm{\scriptscriptstyle ON},\text {sp}}$ at the BV class of 200 V. Compared with the conventional device without HK, the proposed one is in a position to save about 60% of the chip area, while they are having the approximate performance and manufacturing complexity. Hence, the application of HK film is promising to improve the cost performance of trench LDMOS.