Conductive (boron doped) all diamond tips are best suited for use as electrical probes for scanning probe experiments due to their hardness, chemical inertness, and resistivity against wear. In order to overcome the problems of image distortion induced by the tip shape the aspect ratio of the diamond tips was increased to about 7:1 by focused ion beam milling, maintaining a tip radius of typically 30 nm at the apex. The application of these sharpened tips to conducting atomic force microscopy for local electrical characterization of thin metal-oxide-semiconductor dielectrics is demonstrated. Excess current flow was detected at the transition region between the gate oxide and the bordering field oxide due to oxide thinning introduced by the local oxidation of silicon process.