Chemical vapor deposited (CVD) diamond thin films grown homoepitaxially as well as on non-diamond substrates have been the subject of intense investigation since the beginning of the last decade. Diamond's remarkable properties such as physical hardness, chemical inertness, high thermal conductivity, high breakdown voltage, and high carrier mobility are the main factors for the attention it has received from many researchers around the world. Although these properties are somewhat degraded in polycrystalline diamond films, they are still superior to many other materials. One of the most potentially useful applications of diamond thin films is in the semiconductor industry. Although a few prototype devices such as field effect transistors and Schottky diodes have been fabricated on diamond, some major obstacles remain to be overcome before full scale commercial applications of diamond as a semiconductor is possible. The high cost of large area monocrystalline diamond substrates has forced researchers to look for alternative substrates for the heteroepitaxial growth of diamond. So far only marginal results have been reported on the growth of highly oriented diamond films and on the heteroepitaxial growth involving substrates that are as costly as diamond. Silicon, as the dominant material in semiconductor industry, has been the subject of much research as a substrate for the growth of polycrystalline diamond. Another problem in development of diamond as a semiconductor is the effective doping of diamond, particularly for n-type conductivity. Although many researchers have studied boron-doped (p-type) diamond thin films in the past several years, there have been few reports on the effects of doping diamond films with phosphorous (n-type). Once these two issues have been solved, other fabrication steps such as oxidation, etching, masking, etc. may be attempted. The present work is a study directed toward solving some of these problems by looking at in-situ doping of n-type hot filament CVD (HFCVD) grown diamond films on silicon substrates. The study includes electrical characterization, stable metallic contacts, effect of silicon substrate surface pretreatment, and selective area deposition. A number of different techniques for inducing diamond nucleation on Si substrates are studied and the resulting diamond films characterized by common techniques such as Raman spectroscopy, X-ray diffraction, optical and scanning electron microscopy, and profilometery. The effect of doping the diamond films with different concentrations of phosphorous as well as calculation of the activation energy by temperature measurement was also carried out in this work. A new technique is presented for the selective deposition of diamond films onto silicon substrates.