MOVPE growth of InGaAsP using tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) was successfully performed with extremely low V/III ratios. The detailed V/III ratio dependence of electrical properties of InP and InGaAs and optical properties of InGaAsP is discussed. Electrical and optical properties of the epitaxial layers grown with extremely low V/III ratios were investigated for the first time. Featureless surface morphology was obtained for InP grown with V/III ratio of as low as 3. Even with such a low V/III ratio, good electrical properties, net carrier concentrations of less than 1 X 10(15) cm-3 and electron Hall mobilities of higher than 30,000 cm2/V.s at 77 K, were achieved. For both InP and InGaAs grown with low V/III ratios of 1-5, the growth rates were almost the same as those with higher V/111 ratios of more than 30. Good electrical properties of InGaAs were also confirmed. InGaAsP epitaxial layers with lambda(g) = 1.18-1.67 mum were grown with V/III ratios of 1-10. It was clarified experimentally that a lower V/III ratio gave a higher incorporation efficiency of phosphorus in the growth of InGaAsP using TBA and TBP. The photoluminescence intensities and full widths at half maximum at room temperature of InGaAsP/InP double hetero-structures were as good as those grown using AsH3 and PH3.