Diamond's unique properties are potentially superior among the existing substrate materials for electronic applications. Among these properties, diamond's physical hardness, molar density, thermal conductivity, and sound velocity are the highest while its thermal expansion coefficient, compressibility, and bulk modules are the lowest. Because of this unique combination of properties, diamond has diverse applications in electronics, optics, and material coatings. Scientists around the world have been studying possible applications of diamond and its synthesis by chemical vapor deposition (CVD) in the semiconductor industry for almost the latter half of this century. The use of bulk crystals severely limits semiconductor applications of diamond due to difficulty in doping, device integration, high cost, and small area of bulk diamond. Therefore, a great deal of effort has been undertaken by researchers around the world on diamond synthesis by chemical vapor deposition (CVD). With some of the same limitations, homoepitaxial growth of diamond is not considered to be a feasible solution. As a result, heteroepitaxial growth of diamond is being considered to be an attractive possibility. Heteroepitaxial diamond growth has been the main subject of research since the first successful growth of diamond thin films on foreign substrates was reported. Polycrystalline and highly oriented diamond thin films grown on various substrates, especially silicon, have been reported over the years. There also have been reports of device fabrication on diamond such as diamond based point contact transistors, Schottky diodes, and field effect transistors at a laboratory level. The technology has been very challenging and there remain many obstacles to overcome before diamond based devices are to become part of the semiconductor industry. For example, epitaxial growth of CVD diamond, selective doping, n-type doping, and metallization of the grown films are not totally understood due to the polycrystalline nature of CVD diamond films. The objective of this work is the study of hot-filament chemical vapor deposited boron doped polycrystalline diamond thin films grown on both silicon and sapphire. A new horizontal gas flow configuration rather than the typical vertical gas flow configuration is utilized to provide larger area and better quality films grown on these substrates. The study includes characterization of grown films using scanning electron microscopy, Raman spectroscopy, X-ray diffraction analysis, and electrical characterization. Two types of contacts to the films grown on silicon substrates are fabricated enabling various electrical measurements. However, on sapphire substrates, low volume resistivity diamond films are grown despite severe adhesion problems. The effects of various substrate pre-treatments, growth conditions, and doping concentrations are presented.