The surface structures and growth mode of the Cu/Si(100) quenched surfaces have been studied by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM), and the superstructures of 6 × 2, 2 × 2 and c(12 × 10) were observed by LEED mixed with 2 × 1. The combination of these structures depends on segregated Cu coverage which is a function of quenching temperature and deposited Cu coverage. These structures have been analyzed by STM and it has been found that 6 × 2 is an ordered structure of Si missing dimmer defects and 2 × 2 and c(12 × 10) are structures formed by Cu–Si layers with incorporation of Cu atoms into the Si(100) surface. The c(12 × 10) structure was analyzed in detail by STM with changing bias voltage, and a result of the structure model of c(12 × 10) has been proposed, The superstructures on the Cu/Si(100) surfaces do not grow homogeneously, and form the combined domains of these structures, Such a growth mode depending on Cu coverage and quenching temperature is discussed referring to the other metal surfaces on Si.