The 1/f noise of 10 different ungated 2DEG structures based on InP substrates with InGaAs channels was investigated in the frequency range from 0.4 Hz to 100 kHz at temperatures between 80 K and 320 K. In spite of various channel designs (with mobilities between 6470 cm2/Vs and 11800 cm2/Vs), a clear dependence of the total Hooge parameter on the channel mobility was found. From samples with undoped channels the correlation&agr;H&hthinsp;tot∼&mgr;tot−2.6was obtained at room temperature. The lowest Hooge parameter&agr;H&hthinsp;tot≈1.5⋅10−5was observed for the samples having the highest mobilities and is attributed to two-dimensional phonon scattering processes. This value agrees quite well with the parameter proposed by Handel’s theory for umklapp processes. In contrast to this, the Hooge parameter of a sample with channel doping was found to be much smaller due to the presence of impurity scattering. Temperature dependent noise measurements revealed a significant dependence of&agr;H&hthinsp;toton various scattering mechanisms. Considering Matthiessen’s rule and the electron energy distribution, the separation of optical and acoustical phonon scattering as well as impurity scattering allows an exact description of the temperature dependent&agr;(T)H&hthinsp;tot.Furthermore, the Hooge parameters&agr;(T)H&hthinsp;acand&agr;(T)H&hthinsp;optrelated to acoustical and optical phonon scattering processes are found to be temperature dependent material-specific constants. ©1999 American Institute of Physics.