A method of designing a layout of functional blocks and on-chip capacitors in a semiconductor integrated circuit, includes the steps of, in sequence, (a) placing a functional block, (b) placing an on-chip capacitor in an area which remains vacant after the step (a) has been carried out, (c) overlapping a portion of the functional block having been placed in the step (a) and a portion of the on-chip capacitor having been placed in the step (b) each other, if possible, and (d) placing an on-chip capacitor in a vacant area caused by carrying out the step (c).