A microdiamond array, in which 2500 diamond microparticles 2 mu m in diameter were precisely arranged in a mu m scale, was fabricated by site-selective plasma chemical vapor deposition (CVD). Diamond was synthesized on a Pt substrate covered with a SiO2 layer 0.2 mu m in thickness on which, using photolithographic processes, holes of 2x2 mu m(2) were fabricated in order to expose the Pt surface at the bottom of each hole. Diamond microparticles grew selectively on these Pt sites based on the great difference between the nucleation densities of diamond on Pt and SiO2 surfaces. At the initial stage of this site-selective CVD, the diamond growth was confined in the hole, and accordingly, a plate-like shaped diamond microparticle was formed. Using an electrically conductive probe for atomic force microscopy, the electrical conductivity of each plate-like diamond particle was measured while simultaneously acquiring a topographic image of the particles. The diamond particle consisted of multiple grains and their conductivity was not homogeneous. The central regions of the grains were less conductive than their edge regions. The grain boundaries were as nonconductive as the surrounding SiO2 region.