We have studied deep levels in AlGaInP emitter of AlGaInP/GaAs heterojunction bipolar transistor by deep-level transient spectroscopy and photoluminescence (PL) methods.Two deep levels were obtained with thermal activation energies of Ec-Et1＝0.42eV and Ec-Et2＝0.59eV,whose capture cross sections are 6.27×10-17cm2 and 6.49×10-20 cm2，where Et1 and Et2 are Si-related and O-related deep levels,respectively. The relationship between excitation power and PL peak intensity have revealed that nonradiative recombination centers of deep levels exist in AlGaInP.The current gain of AlGaInP/GaAs HBT decreases due to the existence of deep levels in AlGaInP.