Contribution of the impact ionization to the noise characteristics in InGaAs-based HEMTs was investigated by measuring the drain noise current and the electroluminescence (EL). In the measured spectral density of the drain noise current the 1/ f noise becomes more significant at larger drain-bias voltage. Drain- and gate-bias-voltage dependencies of the 1/ f noise intensity were similar to those of the EL data. The similarity in the bias-voltage dependence provides the first experimental evidence for contribution of the impact-ionization-induced holes to the 1/ f noise. Furthermore an expression for the relation between the concentration of the holes and the 1/ f noise intensity was derived. The expression was consistent with the measured result.