  An analogy between the band structure of narrow gap semiconductors and the
Dirac equation for relativistic electrons in vacuum is used to demonstrate that
semiconductor electrons experience a Zitterbewegung (trembling motion). Its
frequency is $\omega_Z \approx {\cal E}_g/\hbar$ and its amplitude is
$\lambda_Z$, where $\lambda_Z = \hbar/m^*_0 u$ corresponds to the Compton
wavelength in vacuum (${\cal E}_g$ is the energy gap, $m^*_0$ is the effective
mass and $u \approx 1.3\times10^8$ cm/sec). Once the electrons are described by
a two-component spinor for a specific energy band there is no Zitterbewegung
but the electrons should be treated as extended objects of size $\lambda_Z$.
Possible consequences of the above predictions are indicated.
