We have focused to grow cubic GaN (c-GaN) on Si(100) substrates using boronmonophosphide(BP) buffer crystals. We have successfully grown BP crystals by MOVPE technique with electrically n-type and thickness deviation is within several % along 2inch wafer under undoped conditions. The electrical conductivity is less than 0.5mohm∙cm. We have preliminary grown GaN by RF-MBE technique, before we carry out mass-producing MOVPE on larger diameter Si substrates. It has been found the cubic type GaN has been successfully grown on the substrates by measuring X-ray diffraction. The crystal quality and defect generation were observed by TEM. It has been found that there are much more dislocations than 109cm-2 generated at GaN/BP interface.