Influence of the valence band discontinuity on the spectral and frequency responses in InP/InGaAsP/InGaAs APDs has been reported. Quantum efficiency showed gradual increases in the wavelength range from 1.0 to 1.3 µm, where the absorption coefficients decrease with increasing wavelength. Frequency response deteriorations, which cannot be explained by usual deterioration mechanisms, were found at around 300 MHz. These two characteristics are due to holes piled up at the heterointerface which was confirmed experimentally. Recombination and thermionic emission of piled up holes cause the deterioration of quantum efficiency and frequency response, respectively. High speed APDs are realized by increasing the electric field of the heterointerface in InP/InGaAsP/InGaAs APDs.