Correlations of metalorganic gas flow rate ratio with solid phase composition and the growth rate of MOVPE-grown AlGaAs using TEG and TMA are investigated. The AlGaAs growth rate is low compared to the sum of individually grown GaAs and AlAs growth rates, and solid phase composition differs from that calculated from their growth rate ratios. These characteristics result from variations in GaAs and AlAs growth rates with vapor phase composition. The correlations among growth properties can be explained by considering the reaction between metalorganic gas sources which reduces the amount of metalorganics contributing to the growth.