New powerful specific test structures are proposed to characterize the thermal resistance Rth of multi-fingered structures including side and thermal coupling effects. The benefit of such structures over standard ones is clearly demonstrated. Thanks to an original method, the derived Rth model is introduced in an NLDMOS SOI macromodel. The global HV model is able to reproduce the DC characteristics of small (widthLt200 um) devices as well as the ones large multi-fingered devices (PA power cell with 1 mm width) without any model adjustments. This method will improve compact modeling approach for multi-fingered devices (HV or not) impacted by self-heating.