A novel thin drift region device with heavily doped N~+ rings embedded in the substrate is reported,which is called the field limiting rings in substrate lateral double-diffused MOS transistor(SFLR LDMOS).In the SFLR LDMOS,the peak of the electric field at the main junction is reduced due to the transfer of the voltage from the main junction to other field limiting ring junctions,so the vertical electric field is improved significantly.A model of the breakdown voltage is developed,from which optimal spacing is obtained.The numerical results indicate that the breakdown voltage of the device proposed is increased by 76%in comparison to that of the conventional LDMOS. A novel thin drift region device with heavily doped N ~ + rings embedded in the substrate is reported, which is called the field limiting rings in substrate lateral double-diffused MOS transistor (SFLR LDMOS) .In the SFLR LDMOS, the peak of the electric field at the main junction is reduced due to the transfer from the voltage from the main junction to other field limiting ring junctions, so the vertical electric field is improved significantly. A model of the breakdown voltage is developed, from which optimal spacing is obtained. The numerical results indicate that the breakdown voltage of the device proposed is increased by 76% in comparison to that of the conventional LDMOS.