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Highly efficient InGaN/GaN LEDs grown on 4- and 8-inch silicon substrates comparable to those on sapphire substrates have been successfully demonstrated. High crystalline quality of n-GaN templates on Si were obtained by optimizing combination of stress compensation layers and dislocation reduction layers. The full-width at half-maximum (FWHM) values of GaN (0002) and (10-12) -rocking curves of n-GaN templates on 4-inch Si substrates were 205 and 290 arcsec and those on 8-inch Si substrate were 220 and 320 arcsec, respectively. The dislocation densities were measured about 2~3×108/cm2by atomic force microscopy (AFM) after in-situ SiH4and NH3treatment. Under the unencapsulated measurement condition of vertical InGaN/GaN LED grown on 4-inch Si substrate, the overall output power of the 1.4×1.4 mm2chips representing a median performance exceeded 504 mW with the forward voltage of 3.2 V at the driving current of 350 mA. These are the best values among the reported values of blue LEDs grown on Si substrates. The measured internal quantum efficiency was 90 % at injection current of 350 mA. The efficiency droops of vertical LED chips on Si between the maximum efficiency and the efficiency measured at 1A (56.69 A/cm2) input current was 5%.