The impact of the high-voltage drift n-well (HVNW) and shallow trench isolation (STI) regions on the electrical characteristics of 32V symmetry and asymmetry n-channel laterally diffused drain MOSFET (N-LDMOS) were evaluated. Asymmetry structure has higher threshold voltage owing to the transient enhancement diffusion (TED) of boron near source region. The smaller extension of the HVNW to STI (E
) for asymmetry structure exhibits a wider safe-operating-area (SOA) from the hot-carrier reliability point of view. To obtain a higher on-current, the E
should be optimized because the steep sidewall of the STI may force current to flow through a longer distance in the HVNW. Finally, increase of EHVNW-STI cannot efficiently increase breakdown voltage.