  We show that zonal flow can be preferentially excited by intermediate-scale
toroidal electron temperature gradient (ETG) turbulence in tokamak plasmas.
Previous theoretical studies that yielded an opposite conclusion assumed a
fluid approximation for ETG modes. Here, we carry out a gyrokinetic analysis
which ultimately yields a nonlinear Schr\"{o}dinger equation for the ETG
dynamics with a Navier-Stokes type nonlinearity. For typical tokamak
parameters, it is found that zonal flow generation plays an important role in
the intermediate-scale ETG turbulence. This finding offers an explanation for
recent multi-scale gyrokinetic simulations.
