Diamond thin films grown on high resistivity, [100]-oriented silicon substrates by the hot filament chemical vapor deposition method have been characterized by four-point probe and Hall effect measurements. The resistivities of both as-grown and chemically etched samples were lower than expected. The Raman spectra showed dramatic changes from two broad bands (one starting at 1250 cm(-1) and peaking at 1350 cm(-1) and the other starting at 1500 cm(-1) and peaking at 1580 cm(-1)) for the as-grown samples to a sharp peak centered at 1332 cm(-1) with a full width at half-maximum of 10.7 cm(-1) for the chemically treated sample. Hall measurements yielded carrier concentrations in the temperature range 180-300 K. From a plot of carrier concentration vs. inverse temperature, activation energies of 0.36 and 0.20 eV are obtained for the two chemically treated samples. The resistivity values at room temperature of 100 Ohm cm are significantly lower than the values recently observed for other undoped samples (p = 10(3)-10(4) Ohm cm). The low resistivity values observed in this work are attributed to the disordered graphitic regions between the diamond crystalline grains.