In high-voltage integrated circuits (HV-ICs) operating at high temperatures, the high electric field spreading out from the high-voltage bond-pad can induce charge transport phenomena in the encapsulation material. A new TCAD-based approach is proposed which is suitable for investigating the role played by the propagation of charge within the plastic mold over the surface of high-voltage circuits. Simulations are compared with experimental data carried out using a dedicated test chip. The proposed approach is able to predict the features of the leakage current curves measured on different sensors during a complete charging transient.