Hexagonal boron nitride (hBN) has been recognized as an important material for various device applications and as a template for graphene electronics. Low-dimensional hBN is expected to possess rich physical properties, similar to graphene. The synthesis of wafer-scale semiconducting hBN epitaxial layers with high crystalline quality and electrical conductivity control is highly desirable. We report the successful synthesis of large area hBN epitaxial layers (up to 2-inch in diameter) by metal organic chemical vapor deposition. Ptype conductivity control was also attained by in-situ Mg doping. Compared to Mg doped wurtzite AlN, which possesses a comparable energy band gap (∼6 eV), dramatic reductions in Mg acceptor energy level and p-type resistivity have been realized in hBN epilayers. Our results indicate that (a) hBN epitaxial layers exhibit outstanding semiconducting properties and (b) hBN is the material of choice for DUV optoelectronic devices. The ability of conductivity control and wafer-scale production of hBN opens up tremendous opportunities for emerging applications, ranging from revolutionizing p-layer approach in III-nitride deep ultraviolet optoelectronics to graphene electronics.