Wide bandgap and ultra wide bandgap semiconductors have received lots of attraction for its application in power electronics due to high breakdown voltage. In addition, wide bandgap also brings the electronic transition energy into the range of the energy of visible light, and hence light-emitting devices such as light-emitting diodes (LEDs) and semiconductor lasers can be made that emit in the visible spectrum, or even produce ultraviolet radiation. Metal–oxide–semiconductor field-effect transistors (MOSFETs) are one of the most important power electronic, and thus interfacial properties of Nitride/Oxide heterostructure are of great importance. In this work, GaN/Ga2O3 and Ga2O3/GaN heterostructure has been grown by molecular beam epitaxy. The properties of semiconductors are shown to depend on its crystallinity and morphology which in turn depend on the growth conditions. Structural investigation of the epitaxial film has been done by RHEED, XRD, AFM, TEM, etc. The effect of lattice mismatch, crystal symmetry on epitaxial layer are also discussed. On top of that, miscellaneous work on PAMBE Ga2O3 has been studied, including homoepitaxy growth of (¯201) Ga2O3 , bandgap engineering of _-(AlxGa1–x)2O3 and annealing study of _-Ga2O3 grown on M-plane sapphire.