  We propose a model of $1/f$ noise in semiconductors based on the drift of
individual charge carriers and their interaction with the trapping centers. We
assume that the trapping centers are homogeneously distributed in the material.
The trapping centers are assumed to be heterogeneous and have unique detrapping
rates. We show that uniform detrapping rate distribution emerges as a natural
consequence of the vacant trap depths following the Boltzmann distribution, and
the detrapping process obeying Arrhenius law. When these laws apply, and if the
trapping rate is low in comparison to the maximum detrapping rate, $1/f$ noise
in the form of Hooge's relation is recovered. Hooge's parameter, $\alpha_{H}$,
is shown to be a ratio between the characteristic trapping rate and the maximum
detrapping rate. The proposed model implies that $1/f$ noise arises from the
temporal charge carrier number fluctuations, not from the spatial mobility
fluctuations.
