β phase gallium oxide (β-Ga₂O₃) is an ideal semiconductor material for power devices based on its ultra-wide bandgap, high breakdown electric field, and easy preparation. However, it is still challenging to realize p-type doping of the β-Ga₂O₃ because of its relatively low energy of valence band maximum (VBM) and flat band dispersion near the VBM, which limits the development of p-n junctions and bipolar transistors. The main strategies for the p-type doping of β-Ga₂O₃ in recent research are based on size effect, defect regulation, non-equilibrium dynamic process, and solid solution. For the β-Ga₂O₃ p-n homojunction and heterojunction, improving crystal quality and reducing the interface defect states are the key issues for optimizing devices' performances. This paper focuses on the p-type conductivity problem of β-Ga₂O₃, systematically reviews the electronic structure of β-Ga₂O₃, the experimental characterization and theoretical calculation method of doping levels, the reasons for p-type doping difficulty, and the breakthrough in research advancements for improving the p-type doping of β-Ga₂O₃. Finally, the relevant studies on the β-Ga₂O₃ p-n homojunction and heterojunction devices are briefly reviewed. It requires further exploration to realize p-type doping of bulk-phase β-Ga₂O₃ through complex-defect regulation, non-equilibrium dynamics, solid solution, and combining these schemes. The device performances of p-n homojunction and heterojunction also need further optimization.