In this paper, we present an analysis of the degradation induced by hot-carrier stress in new generation power lateral double-diffused MOS (LDMOS) transistors. Two architectures with the same nominal voltage and comparable performance featuring a selective LOCOS and a shallow-trench isolation are investigated by means of constant voltage stress measurements and TCAD simulations. In particular, the on-resistance degradation in linear regime is experimentally extracted and numerically reproduced under different stress conditions. A similar amount of degradation has been reached by the two architectures, although different physical mechanisms contribute to the creation of the interface states. By using a recently developed physics-based degradation model, it has been possible to distinguish the damage due to collisions of single high-energetic electrons (single-particle events) and the contribution of colder electrons impinging on the silicon/oxide interface (multiple-particle events). A clear dominance of the single-electron collisions has been found in the case of LOCOS structure, whereas the multiple-particle effect plays a clear role in STI-based device at larger gate-voltage stress.