In this letter, fin-shape tri-gate <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga2O3 lateral MESFETs are demonstrated with a high power figure of merit (PFOM) of 0.95 GW/cm2 - a record high for any <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga2O3 transistor to date. A low-temperature un-doped buffer-channel stack design is developed which demonstrates record high Hall and drift electron mobilities in doped <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga2O3 channels allowing for low ON resistances (RON) in <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga2O3 MESFETs. Fin-widths (Wfin) were 1.2-<inline-formula> <tex-math notation="LaTeX">1.5~\mu \text{m} </tex-math></inline-formula> and there were 25 fins (Nfin) per device with a trench depth of <inline-formula> <tex-math notation="LaTeX">\sim ~1~\mu \text{m} </tex-math></inline-formula>. A <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga2O3 MESFET with a source-drain length of 6.4 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> exhibits a high ON current (187 mA/mm), low RON (<inline-formula> <tex-math notation="LaTeX">20.5~\Omega </tex-math></inline-formula>.mm) and a high average breakdown field (4.2 MV/cm). All devices show very low reverse leakage until catastrophic breakdown for breakdown voltages (VBR) scaling from 1.1kV to ~3kV. This work demonstrates the potential of channel engineering in improving <inline-formula> <tex-math notation="LaTeX">\beta </tex-math></inline-formula>-Ga2O3 device performance towards lower conduction losses for low-to-medium voltage applications.