  Heterosubstrates have been extensively studied as a method to improve the
heat dissipation of Ga$_{2}$O$_{3}$ devices. In this simulation work, we
propose a novel role for $p$-type available heterosubstrates, as a component of
a reduced surface field (RESURF) structure in Ga$_{2}$O$_{3}$ lateral
field-effect transistors (FETs). The RESURF structure can eliminate the
electric field crowding and contribute to higher breakdown voltage. Using SiC
as an example, the designing strategy for doping concentration and dimensions
of the $p$-type region is systematically studied using TCAD modeling. To mimic
realistic devices, the impacts of interface charge and binding interlayer at
the Ga$_{2}$O$_{3}$/SiC interface are also explored. Additionally, the
feasibility of the RESURF structure for high-frequency switching operation is
supported by the short time constant ($\sim$0.5 ns) of charging/discharging the
$p$-SiC depletion region. This study demonstrates the great potential of
utilizing the electrical properties of heat-dissipating heterosubstrates to
achieve a uniform electric field distribution in Ga$_{2}$O$_{3}$ FETs.
