This article systematically explores the design space of beta-(AlxGa1-x)(2)O-3/Ga2O3 double heterojunction field-effect transistors (DH-FETs) for high-power applications using a well-calibrated TCAD setup. It primarily focuses on the impact of various intrinsic device parameters on DH-FET performance, including barrier layer thickness, delta-doped layer doping concentrations, spacer layer thicknesses, channel layer thickness, UID layer thickness, gate-to-drain contact spacing, and trap concentration. This study thoroughly examines the effect of these parameters on the on-and off-state characteristics of the device, offering valuable physical insights. For each parameter, the investigation primarily assesses its impact on on-resistance, off-state breakdown voltage, threshold voltage, and resulting power figure of merit (PFOM) as performance indicators. This study would serve as a helpful resource for designing high-power beta-(AlxGa1-x)(2)O-3/Ga2O3 DH-FETs and offer important guidance for the future development of Ga2O3-based heterostructure devices.