The inherent fluctuation of electrical properties in a fine semiconductor region has been successfully reduced for the first time by implanting a small number of dopant atoms by means of single ion implantation (SII) which enables us to implant dopant ions one by one into a fine semiconductor region until the necessary number is reached. Trimming of the conductance of a fine resistor which corresponds to an active region in semiconductor devices has been tried by using the SII. Firstly the conductance increase per one dopant atom in a sub-μm scale Si resistor was measured to be 18 nS/atom. Secondly very fine test resistors with a size of sub-μm were made by conventional device fabrication technology and the statistical distribution of conductance in the test devices was obtained. Then the number of single ions necessary to trim the conductance value to a certain value in the higher side of the initial distribution was implanted to each test resistor. The initial conductance fluctuation of 63% has been reduced to only 13%.